I've addressed the issue of young instructors in a previous article, called "Racism in the Martial Arts." There, I talked about what I call the self-inflicted inferiority complex that we have as Westerners to our Asian counterparts regarding rank. In essence, it's perfectly acceptable for Asian martial artists to achieve high rank at a young age but taboo for a Westerner to do so. As stated previously, the criticism and ridicule of young martial artists usually comes from practitioners who have been in the arts several decades and have reached a point where their advancement comes to a halt, for a multitude of reasons. Perhaps their instructor has passed away or retired, and they do not want to accept rank from anyone else. Perhaps they've broken away from their organization and have no one to promote them. Perhaps they were overlooked for advancement. Whatever the reason, their criticism is solely based in jealousy and nothing more. Surely because they may not have been mature enough or had the opportunity to progress that quickly, anyone who does so must be a fraud.
The fact of the matter is simple. With the extreme variability of rank requirements across the board, along with the wide range of personal capabilities (physically, mentally and spiritually) among people in general, it is not far fetched that there will be those of young age who possess not only the physical knowledge but the maturity, understanding and dedication to be worthy of high rank and license. As long as their rank and license has been earned legitimately, who are we to question them? Twenty years in the arts is the same time frame of experience whether it's from age 4 to 24, from 18 to 38, or from 25 to 45.
If you truly want to know where someone stands in the martial arts, get on the mat and train with them. On the mat is only place you can't lie about what you know. If you do come across someone younger that outranks you, before judging them, talk to them. Train with them. You may just be surprised.