What's the phrase for things that get better with age?

It could be said that it matures with age.

I think of the word mellow. From NOAD:

mellow
adjective
1 (esp. of sound, taste, and color) pleasantly smooth or soft; free from harshness: she was hypnotized by the mellow tone of his voice | slow cooking gives the dish a sweet, mellow flavor.
2 (of a person's character) softened or matured by age or experience: a more mellow personality.

It can also be used as a verb, meaning to become mellow.

If you're talking about things seeming to get better with age, that would be nostalgia. As for things actually getting better with age, that's just my wishful thinking.