All of the surgeons I've talked to said it's fine to not have started T when you get surgery.
The only reason it's "better" to do it after T is because T can decrease the size of your chest by redistributing fat and increases the muscle underneath it. But I don't think it makes a gigantic difference, and as Doc pointed out it may be beneficial in other ways not to start first. And you can always do push-ups.
I've also heard that you have to go off hormones before surgery... but I may have misheard that.