The first time I read your post I missed the parenthetical in the first paragraph, and was inclined to agree with you. Then I looked again and saw "(late twenties)", and had to laugh.
On the one hand, you're right, you can't learn everything. On the other, to be able to realistically claim that you can pick up new languages quickly, you should already know three or four different kinds of languages. If all you know is Java, you probably are farther away than you think from picking up a very different language like Ruby. I would encourage you to do some study on the side. Your late twenties is far too early to let yourself get pigeonholed.
On the one hand, you're right, you can't learn everything. On the other, to be able to realistically claim that you can pick up new languages quickly, you should already know three or four different kinds of languages. If all you know is Java, you probably are farther away than you think from picking up a very different language like Ruby. I would encourage you to do some study on the side. Your late twenties is far too early to let yourself get pigeonholed.