LaserCaps

It all depends.  Maturity level does play a bit into this.

Moving fwd when you're too young is something that has been discussed ad nauseam. Doctors will typically want to avoid doing anything until the pattern reveals itself.  An example I like to bring up is one of a young man who's in the process of maturing his hairline.  He convinces a doctor to fill in the temporal areas which are currently in the middle of his forehead.  The patient is destined to lose all the hair on top within 10 years.  He'd be left with two horns worth of hair and nothing else.  It would be nice if we had a hair crystal ball from time to time.

But you can also consider a young man, say 19, with already a very advanced pattern.  Why would you wait?  (In cases similar to this the first thing that's typically recommended is the use of medical modalities to help the patient retain and enhance the native hair.  A year later, depending on the outcome, and if the patient has available donor, he might be able to do something. 

Lastly, consider the non surgical program. We know testosterone is what drives guys and this is broken into DHT which we know is an irritant to the follicle.  But DHT is important in early development.  So, when it's the right time to prescribe these to a patient.  Early 20's?  

Difficult question if you think about it.  It all depends on the situation.