I don't think it's the age, it's the other life obligations.
In my early 20's I was in college. Graduated in 2008 in to the recession and was lucky to have _any_ job. Spent all of my nights learning coding.
In my mid-late 20's, starting in 2011, I finally got a crappy job with a pay cut in tech (sort of) doing ad operations. I worked hard and spent the evenings getting better at Java so I could use the Dart For Publishers SDK to automate things I hated doing at work (inadvertently helped the company make about a million extra bucks that year, I later realized).
In my early 30's, I got married, changed countries, became a Technical Account Manager, studied Python and German in my free time, and eventually became a dev for a video game company.
In my (our, now) mid-30's, we had a kid, and now I spend my free time on that and house repair, etc. I still like coding but after dinner, bath, bedtime stories, maybe 15 minutes chatting with the spouse, and then other chores, I'm going to bed (before anyone asks, I watch 0 TV and do very little by way of social networks).
I have a colleague who's in his late 20's, no kids, and he's on Slack all. the. time. He talks about stuff he worked on (for work, not for hobbies) over the weekend. I don't think I produce as much as him, to be honest. Makes me a bit anxious about where I stand - hard to compare my 40 hours to effectively his whole life.
I think I need a plan B.
(Related discussion - and the article is 10 years old so the young'uns then are getting in to their 30's now)
https://news.ycombinator.com/item?id=9361580