Gonna pile on some more since the op is probably more confused than ever (if he is still reading):
In a given distance, white ranch will have 2x vertical and 6x technical vs NTM. But there are some dirt roads from the top parking lot if your son finds he isn't up for the craziness (you will both hate the first 1/2 mile from the lower lot).
Cool things at WR: historic farm stuff, open meadows, views over the top of NTM, more mountainy.
Cool things at NTM: the south side runs along the coors brewery which is truly massive, people may be climbing, views of golden on the west and denver on the east, and best of all: golden bike park!
That should be all you need to decide where to go. Either way be sure to finish it off with a jackwaggon from d'deli in downtown golden.
Edit: took out some snark since op said he's advanced