I won't speak to opportunities; I agree with you that there's a lot to be said for specialization. But, to the point about getting older: There's a fair amount

I won't speak to opportunities; I agree with you that there's a lot to be said for specialization. But, to the point about getting older: There's a fair amount of evidence that learning new, challenging (as in, outside your comfort zone) things is a big part of maintaining your mental acuity as you age. Doing crosswords is good for your brain, but only if you're relatively new to them. If you've been an avid crossword puzzler for decades, not so much. Learning a new natural language is another example of something that is supposedly good for keeping the creative juices flowing. I wouldn't be surprised if challenging oneself with a new programming paradigm behaves similarly. Which would mean that learning Haskell might make you a better Rubyist, not because (as people often like to say) Haskell teaches you specific things that you can't learn while using Ruby, but because the mental challenge of learning to work with such a drastically different programming language just generally helps keep you sharp. That said, I would not go so far as to speculate that this effect is any greater for learning a programming language than it is for learning Esperanto. Just pick the one that sounds more fun.