I'm 22, got a pair of nice cufflinks (along with a "cufflinkable shirt" - something I didn't have... they would've been useless to me otherwise) for my 20th and a pair of guitar-shaped ones for my 21st. Don't exactly wear them often, only to the odd dinner, wedding or other fancyish function. I find them nice to have though.
Love the guitar ones, though admittedly I'm the type who like novelty items like that... Got a pair of anchor-shaped ones for a mate of mine who is into his sailing, and he loved them (or so he says...)