The Harry Potter Lexicon is your friend ! (And mine, don't worry.)
Yes, both Hagrid and Voldemort are not that young. However, keep in mind that wizards' lifetime is about twice the Muggles'. See how Aunt Muriel is (in DH, she's 107), или Dumbledore who died (prematurely) at 115 или so.
Besides, Hagrid is a half-giant. Giants may have a longer lifetime. According to the Lexicon, he would have been born on Dec. 6, 1928. So he was a young student when Tom Marvolo Riddle was a prefect.
As for Voldemort... he almost died a first time (in 1981, courtesy of Lily's sacrifice to save her son). He came back from almost nowhere in 1995 (in the infamous graveyard scene). He had undergone so many transformations throughout his life due to Dark Magic that he's got practically nothing human left. According to the Lexicon, he's born on Dec. 31, 1926, so he was 71 when he died for good in May 1998.
Of interest : Minerva McGonagall was born on October 4, 1925, according to the Lexicon.
Here's the link to the Lexicon, for any future references - that's useful ! :
link