I don't think it's at all about age. I think it's about personality, whether someone sees a need for learning a particular thing, whether someone has the time to spend learning something new (and whether not having time is even an option because the new thing is iimportant to learn), whether someone has so many worries/concerns he can't make himself be interested in anything but those, whether someone can afford to learn what he'd like to learn, whether someone has so many responsibilities he has a hard time find the time and "mental energy" to seek out learning something new, whether a person goes through life resistant to learning what he runs into by accident, whether a person wants to learn over his whole lifetime and/or whether what the new thing is something he sees as valuable or worth learning (or not bothering); or probably any number of other factors.
I think most people are pretty much the same person when they're older than they were they were younger. It's just their life that becomes fuller and/or more complicated, and that what they learn from life can change their perspective about what's important, what's worth sacrificing time/effort, etc. Younger people sometimes are trying to "find what they're good at" by learning new things (sometimes just for the sake of learning/doing new things, but sometimes for reasons like enhancing a resume). So I suppose someone older may be less prone to "dabbling" in learning new things; but, still, I do think it's largely a matter of personality.
Of course, too, one person may keep learning about one subject throughout his whole adult life, rather than "diversify" his learning. Someone else may want to learn a little about a lot of things and not devote all his learning/thinking/growing time to (primarily) one subject. Older people also may feel sure enough about who they are to say, "I'm not interested in learning to play basketball because I didn't care about it when I was twenty so I sure as heck don't care about it now." So maybe it's more a matter of people growing more selective and sure about what they want to learn as life continues. I just really don't think it has anything to do with age, by itself.