I would relate it to other fighting arts. I think professional boxers are usually less than 30 years old but a few have done well at 40. A 60 year old boxer may have better understanding so as to be able to generate the next champion. I have heard that some 70 year old fencers can give the young guys a run for their money but the Olympic champions are likely to be guys also less than 30 years old. Good Wing Chun at age 60 can handle bad Wing Chun at any younger age within certain physical limits of speed , size and strength. We always have limits.
Ray
Victoria, British Columbia, Wing Chun