I can relate to that -- perhaps it's a bit the feeling of "missing out", like, when your peers have the time (and energy ;-)) to do fun stuff that you just cannot do because of the kids.

But I'm thinking that I had ample time to make experiences earlier in life, and even though I'm going to be close to retirement age by the time the last one of our children is going to leave the house, I still think it was fine the way it happened.

The whole framing of "I'm missing out because I have kids" is already a pretty terrible way of thinking about life, to be honest. I have a good friends who's divorced and with pretty much no circle of friends, apart from me, and he's really having a hard time coping with loneliness. Me, on the other, I cherish each chance I get to spend some alone time where I can just do hobby stuff or whatever, even though these moments really don't happen very often.