A few =/= AllExplain why all the best athletes around the world are mid 30's then? But hey, don't let facts get in the way of excuse making for Federer losses.
Other sports =/= Tennis
Also you said 40, not mid 30's. Moving the goalposts already?
Tennis has been getting older since the mid to early 00's but for every Federer there's a Ferrer, Berdych, Tsonga, Gasquet etc...who all declined in their early to mid 30's. Saying there's no reason not to peak until 40 is delusional at best.