I'm not sure if you mean to change in his tone, timbre. If that's what you mean then peoples voices naturally change with age.
Singers more so because they use them more. This is the case for every singer i know. You lose a couple of top notes but gain in timbre and strength and also get a couple of lower notes.
My own voice has dropped in tone and i can reach a few more lower notes than i used to when i was in my twentys.
Is that what you mean, his vocal range, timbre etc?