And think about it, if you always wanted the same things in life, you wouldn't be growing as a person.
Do 12 year olds look back and say, "oh man, going on a roller coaster while eating a five pound bag of sour-patch gummy bears will never be as good again as it was last year..."?
I don't want to go on roller coasters and eat gummy bears. I am not 11 years old anymore.
If you are able to grow emotionally, you find other things to love and enjoy that are just as good in their own way as what you were doing at different stages of your life.
At +50 you can support your kids and hopefully someday grand-kids. You can invest, buy property, travel, eat better, try new sports, etc.
You can't run 1500m PRs, but that's okay, there are other things in life as wonderful as the 1500m.