I think I'll have to disagree with you there @MiksuSH. While I have argued in the past that Billie's voice has worsened quite considerably in terms of tone since the 21CB tour, I think it's less down to age per se and more down to lack of adaptive technic. He isn't taking care of it as much as he should and not stimulating the vocal chords to counteract some of the effects of ageing and the prior drugs/drinking. He also might well have got used to singing a certain way, when drunk or on drugs, but then not adapted his technic, now that he's sober and older.
However, despite a difference in tone and slight pitch-problems, he is still more than capable of singing his songs and is one of the best sounding and consistent front-men of his age group, to this day.
As to them not being able to play fast songs anymore, I strongly disagree with you on that one. Tre certainly looked a little tired and exhausted on the last tour, most probably a combination of ageing and lack of exercise, but he played the songs flawlessly. In fact, he's more consistent with his tempo now than ever.