[pen2l]

Don't think it works like that.

Rather, it's that you have only so much time to dedicate to things... if you're focusing very much on one, then you're not spending time with the other -- and overtime, you'll lose that other thing. If you can manage to spend a good amount of time on two things (let's say, learning a new instrument and learning a language) everyday, consistently, then you will get both.

[colordrops]

It does work like that. As you get older your ability to retain information wanes.

[Apocryphon]

That could be physical degradation from age, not necessarily the "running out of disk space".

[colordrops]

Why does the cause matter?

[Apocryphon]

Because if it's simply because of physical degradation, that means someone can keep on learning and not worry about running out of memory.

[colordrops]

If your memory doesn't work, what does it matter how much you have?

You can create ungrounded abstractions all you you want, but as an older person who has commiserated with other older people, the common conception that it's harder to learn and retain things in older age is a real thing

[Apocryphon]

Sure, but what you're describing is the difficulty of learning as age sets in. That's very different from the original assertion- "If I start specializing elsewhere I'll forget the intricate details of the thing I'm already specialized in." - unless that person was describing themselves as older.