I think others have covered what I was going to type.
While we await western medicine catching up with TCM regarding time spent stuyding pu-erh then I'll stick with the TCM guidelines.
By sticking with the guidelines I mean drinking whilst being aware that there may be potential downsides, much as I smoke or drink alcohol.
I suspect a large scale scientific experiment might prove that loads of young sheng can give you a sore tummy.
The other issue is that a proper scientific study is unlikely to be around for some time. As in a study of 1000 people drinking sheng over 5 years showing little ill effects will provide little light on the effects of one person drinking it daily for 50yrs.