However, now I am in my sixties friends who are a little older who couldn't or didn't have children and never regretted it up to now are feeling the loss and mention it continually. It is not just the 'who is going to look after me?' argument either. We also notice that they are different from our friends with children. It is as if having children allows you to mature and move on and there is a deep happiness and satisfaction with life when there is another generation (or perhaps too) to carry on.
You say you are 'not being judgemental', but you claim that the difference between your friends with children and your friends without is that the former have 'matured and moved on' and are more deeply happy and satisfied with life -- and the friends without children are thus, by your reckoning, comparatively immature, have not 'moved on' (whatever that means), and are less happy?
If that's you being 'non-judgemental', I'd really hate to see you when you're being judgemental.
Depressingly, you are just reinstating a load of tired old stereotypes about how not having children means you haven't fully engaged with life.
I was almost 40 when I had my son, and I'm pretty much exactly the same person I was before I had him. He's a new person to love, as well as a new responsibility, but I don't buy the stuff about motherhood fundamentally changing you. I certainly haven't. Maybe it's different if you have a child very young, when your adult character is still emerging, or if, for some reason, having a child takes your life off on a very different trajectory to how it would have proceeded if you didn't.