I think the issue here is not learning new things, but having the time to sit down and focus on them. As a child and young adult, you usually have fewer distractions -- whether a significant other, a mentally or physically exhausting job, bills to pay, etc. -- and spending hours on a single task is not so difficult.

I have found a lot of success in waking up earlier to do the "learn a new thing" part of my routine, before the hectic work day begins.