In my humble opinion, Eddie Izzard used to be extremely funny 15 or 20 years ago but these days, not so much.
Generally speaking, people's musical and comedic creativity peaks around 30 years old. Obviously, this is a huge generalisation and there are a number of notable exceptions but on the whole, this seems to be the case. Why? Who knows but when you look back at the 'greats' in both music and comedy, it's rare to find someone who is making ground-breaking art in those genres when they're in their 40s, 50s and 60s and beyond. Almost invariably, their best work is when they're in their 20s and 30s.