As someone who used to box off and on from childhood to early adult years,as well as known countless fighters, i have to say you are wrong... You do get rusty and timing,speed,snap fades.. But once back in training someone with past experience, has a huge headstart on a total beginner.... Almost comparable to riding a bike, throwing combonations on call,hitting the bags,and various training routines comes back to you... Also the instinct of what moves to do at certain times becomes 2nd nature... I havent seriously trained as a boxer for over 20 years, but compared to a beginner if we were to get in the ring.. Id be many steps ahead.... For some it takes alot of time and effort to get those fundamentals and moves down to being like 2nd nature,, but once learned you wont forget, especially when your older.. The younger you are the easier it seems to pick things up quicker.