The main impact of age is the mental and physiological tear and wear. While he has some back issues that came and went, a small ankle issue years ago and a minor knee surgery, he is by and large in great shape and probably will still be for several years. Stamina, strength and coordination are hardly affected with aging. Recovery time is more of a problem, but it should not be in a Grand Slam on grass. Mentally, he showed both his hunger and love of the game time and time again and apparently loves the constant travelling around the world (which is the most draining thing for many). I guess that being able to afford to travel with his whole family and use the best transportations and accommodations available helps!
Federer's main problem is not that he is older than just about everyone in the draw, it's that this past week in Halle he just did not play very well. His offensive play lacked creativity, the net play was at time a bit dubious and the backhand was a liability, especially when it came to passing shots. He nailed a couple critical ones on key points, but, most of the time, his opponents could go to the net without much worries after attacking his backhand. For the positive, the serve and forehand worked ok.
It's difficult to assess Federer's chances without seeing if some rest and training will help him play at a better level in Wimbledon. As far as the draw go, there were some low seeded or unseeded floaters that you wanted to avoid. He avoided Djokovic, Murray, Kyrgios and Lopez, but he has Karlovic near him (3rd round potentially), Coric who played an extremely good match in Halle's final to beat him (4th round) and Querry or Muller potentially in quarter (along Anderson or grass lover but somewhat less menacing Gasquet). On paper, the opponent in the semi would be a very much in form Cilic. Not the worst draw for sure, but first thing first: let's see how he fares in the supposedly 'easy' first couple of rounds against Lajovic (a clay / regularity player as far as I remember) and Lacko or an unkown french qualifier.