This sounds sensible. Can you give me an example or two?
Most of them are not like definite plans but rather taking mental notes.
Anyway, here are few examples.
During my early 20s:
People in my circle who were in 30s wished they got married and had children in late 20s or early 30s.
Many wished they completed their studies (masters or PHD) before hitting 30 (or before getting married or before having kids).
During my early 30s:
People in 40s wished they had 3 children instead of 1 or 2. Family support or their financials restricted them.
Many wished they started their investment journey lot earlier.
Many wished they gave first preference to their health.
Almost 40 (now):
Many say how they missed their children's young age (say up to age 13). They wish they spent more quality time with them.
People in 50s are not really in a demanding position at work.
People who didn't participate in group sports or serious hobby are kind of struggling as their children grow older.
Above may not be suitable for everyone or fit everybody. I guess, we tend to notice more about the things which are important to us.