You are not over qualified because you are over 35.
So are you asking when do you need to start to work on your weakness?
Or are you asking when do you stop working on lifting hard and heavy?
Personally I believe it has to do with injuries, if you are always injured or getting surgery it may be time to change your approach. Some Genetics are made for big weights for longer than others.
When you have to decide if pulling or squatting is putting you are your back for a month is it really worth it for quality of life?
Also personally I believe you should always work on your weaknesses, cause if you do not you will plateau on heavy weights anyway.