true, but like fuji said you need to define what you mean by proficiency. if it's WWC/EWC olympic level, then yes you most definitely need to start training pretty serious at age 9-10. however, if by proficient you mean something less spectacular, it can totally be done even when starting at a later age.
and dont mention Lu here as an example he probably had better technique as a track & field guy than most US (or finnish) lifters already.
it seems you have little exposure to actual strength athletes' programming. lower intensity days and proper periodization is important as shit. and this is in reference to ppl who go to the olympics so if they do it it's most likely worthy to consider for a weekend warrior.