dunno about that......im the best part of 95kg and 6'1'', and have no problem in any GA a/c i've ever flown in. Also, I fly gliders which are dubbed as cramped from the front seat, yet I have no issues at all and I have very broad shoulders. I've seen guys a fair few inchs taller fit without control issues, so you should be fine
As for being fit, you should want that anyway. Fine we should all adopt healthy lifestyles, but also look at the bigger picture. You could find yourself in years to come finding it difficult to renew a Class 1 on the grounds of high blood pressure for example, and suddenly a little investment of time into exercise is tiny compared to the investment you had to make to get the licence in the first place
