Can a hair doctor predict future baldness in young man?

Predicting future balding

It's possible to predict future balding fairly accurately for men in their 40s. Prior to that, it is not possible to predict accurately, However, it is possible to speak in terms of one's chances, odds or probabilities.

For example, I might tell a patient:

• "Based on your history and current progress there is a HIGH chance you'll bald to a Hamilton Norwood stage 5"
• "Based on your history and current progress there is a LOW chance you will bald beyond Hamilton Norwood stage 3"

Family history is complicated and is not a definite guide. But yes, men with a father who is HN6 have an increased risk of balding. In a study of 572 men ages 16-91, young men with a balding father had a 5.5 times increased risk of balding thanyoung men who did not have a balding father.
In another study, only 1 of the sons of 50 non balding men had Hamilton Norwood type III balding or worse. In contrast, 32 of 54 (60 %) of sons whose fathers were bald had Hamilton Norwood scale type III baldness or greater. 

Clearly, having a father with balding greatly increases the chance a given male with develop male pattern baldness. 

References
Birch MP Eur J Dermatol 2001; 11-16
Ellis JA. J Inv Dermatol 1998 110: 849-53