Awww sweetie. I've been estranged from my messed up family for 29 years. Yes, I have 3 kids, but I also have a family of FRIENDS that rival any blood family you could hope for. Message me if you want to talk about ways to find your "framily" (friend family).

I have no family to speak of. Parents gone, majority of my siblings gone and I'm not in relation with the last two living ones, no cousins to speak of.....come from a very dysfunctional background. I broke those chains so I am the one who has removed myself from those family ties. I have two children who are doing well in life and while I know they'd do anything for me, I don't want to burden them. As for DHs kids, if DH goes first, I'll never see his kids again...and I'm okay with that. We aren't in relation anyway so no loss to me.

My family has been built via my friendships. My "girls" are my family and I am theirs. We take care of each other. Begin to build a group.....whether that is thru a hobby (I quilt), volunteering (I volunteer in dog rescue transport and network with a charity organization in my community), church (Sunday and small group studies), sports (bowl, kayak), gym. Through these avenues, I have built a strong network of dear friends and we look forward to walking into old age together. 

Find something that interests you, get involved and you will make friends.

It’s a scary thought that’s for sure, but reality is even if you did have family or children it’s best not to count on them.  I’ve learned some hard truths in my life recently, that despite having DH, my kids, my family and friends I will have to be the one taking care of me when I get older.  Start thinking ahead, look into writing up a future health care plan, work with a lawyer to lay out what you would want done for you as you age and if you are unable to make your own medical decisions.  Look into assisted living facilities and set up where you think would be best for you.  If you have close friends, discuss this with them, talk about if they could be a support system as you get older and lose certain facilities.  I think what makes it so scary is the unknown, so don’t let it be unknown, start making a plan now.

The positive thing is that you will be in good company. There are and will be thousands upon thousands of women who are or will be widowed and childless or disconnected from their children/step-children/families of origin. 
I completely agree with what others have said:  Get involved now in activities that interest you. Some of the best friends I have made in life came through exercise classes. I like volunteering when I can; relationships seem to be made so naturally in those situations. Meetup groups are a great way to meet people (and, yes, they have them sometimes grouped by age). I am sure there are widow/widower support groups everywhere. Places like YMCAs have all kinds of activities scheduled for seniors. You really will not be alone. There will be many of us "out there" in similar situations.

So parents are not in the equation.   Unfortunately you will out live a lot of friends. It's  not the golden years.  It's the doctor years.  It's important to have money.  Money help in getting help, ect. Think about Assisted Living Facilities where they gave rec rooms , clean do meals. 

My 101yo mother lived in an assisted living community for 6 years and, unexpectedly, loved it.  Her community had 3 types of housing: cottage duplexes, an apartment building + dining room and a building for those with greater daily medical needs.  She progressed through all 3.

This type of situation provides easy access to new friends, if you wish.  There is help available, both medical and practical, if you need it, altho many live as independent adults.  Ours had many activities, ranging from card games, barbecues to her fave, happy hour each Friday.  She had a male friend, a widower with only 2 relatives, a son and sister.  Both died of covid so he had no one but at least he had the people there.

If you can afford it, these communities are an exvellent alternative for older people.  When the time comes, you can shop around to see which fits best.  I, myself, am considerig this, depending on how things go with DH.  I dont want to depend on my bios and can't depend on SD.

Here's something to keep in mind:

As a woman, you will **always** have suitors.  They may not be the 10/10 Chads that you want to date, but they may be good for companionship.  And obviously, you will be able to get sex any time your want, if that is something still important to you.

The ideas about hobbies, church, charity, etc. that others mention are good too.  You may have to combine several things to feel fulfilled and busy. 

I work 80+ hours a week between my main job and side buisness, so I can't even imagine what it would be like to have free time, although I hope this isn't always the case.

I know several older women, one of them my good friend, who are living with their friends who are also single and don't give a hoot about being married or meeting another partner. Two ladies just bought a house together in our neighborhood, super nice, not lesbians, but got sick of condo living and dumped the city. I can see myself doing this in the future too! 

This is something that I have also considered, thought about, obsessed over and part of my whole "sour grapes" routine I get mired in every now and then. Kind of like the "smug marrieds" in Bridget Jones Diary, I think of bio parents as the Smug Parental Units. Good for paying and contributing, all in hopes the kids will consider them in their old age.

Meanwhile, I get to watch Toxic Troll and Husband fail as parents, but get all the love and loyalty. I get to still pay and support, but without benefit.

My Gfs and I speak of this, among ourselves. The bioparents are expecting (sort of) their kids to take them on in some capacity. One friend bought a house with the thoughts that she could grow old in it and someday someone would be in-house care when she would need it.

Ive put myself through the wringer thinking of "what ifs" about when husband expires. My community is small. Im social. Im ready to start running again and want to get into more athletics, and build closer connections. My big limitation is finances and proximity. I live 30 mins from my community and it doesnt sound like much, but there is also a "class barrier". No one likes to visit my town that I live in. Its dusty ag town, in proximity to multi-million dollar properties, so I feel isolated. Possibly of my own making.

Just know you are not alone in this. Just another flavor of suckage in stepland.

I would be lying if I didnt say that I  hadnt had concerns that echo yours. I am already having reason to worry that one of these days I will end up completely alone, and will have no choice but to be backed into a corner where I will have to soley depend on SD to "take care of me when i get old". I already mentioned on a post by JRI ( @JRI excuse the repetititon)  that out of the blue SD29 had that expectation completely unbenowknst to me. I shoudnt be findting this so unnerving but if you knew my SD youd get it . The girl can barely get her own life together but wants to take on that level of resposbilty for mine. I dont know why shoe would assume that I would allow that. Acts like I agreed to it or that I should . But I dont want to. since I am . Just not comfortable with the idea. To he honest, even if I had my own kids and even if SD and I had the most perfect relationship, I still wouldnt have planned for that because I woudnt want to burden anyone. ..But all the other posters have offered lots of good options to consider for you and others in our shoes...I say we all figure it out togehter. 

I also have seen first hand in my own extended family that its not a 100 percent foolproof promise that all kids can be depended on to take care of elderly parents. Or may not have the means or the resources to do so no matter how much they want to take that on. Assisted living places and the like exist for a reason.  Sad as it sounds, it doesnt always work out that way.