Some of these comments are a bit harsh. This isn't about the amount of money he has but the fact that he is being forced to give up something he loves doing because of injury. Yes, the older you get the higher chance of injuries and a long recovery if at all from these injuries.
I feel for him, and sad that he has to give up but he should be proud of what he has achieved, twice winning Wimbledon and Two Olympic gold medals. Something we haven't achieved in this sport for a very long time.