I'm withholding judgement for the time being. The problem as I see it is that any person who does well will be under scrutiny, so to an extent the whole thing becomes meaningless. Froome was under suspicion for winning the Tour, Horner for winning the Vuelta. I didn't follow the coverage at the time, but I'll bet someone accused Nibali of cheating when he won the Giro. Anyone who cycles well is under suspicion, so you can't really single any one person out as being more suspicious than anyone else.
As for his age... Hey, maybe he's just some freak outlier, and all the stars aligned for him. Most cyclists don't win anything much at his age, but every once in a while, it could happen. It's not impossible. To an extent sport depends on chance factors. Maybe he's genetically pre-disposed to peak at this age. Maybe his injury and the pattern of his season allowed him to peak at that point in the season compared to everyone else. Who were his main competitors? Nibali? Rode the Giro. Rodriguez and Valverde? Both rode the Tour. Maybe he just got lucky that he was fresh when his competitors were tired.
I'm not saying it isn't amazing for someone his age to win, but it is not outside the bounds of possibility, and until we see more evidence we can't really say for sure. It's not like he's 75 or riding with one leg or whatever.