Hard luck bro, it sounds tough but I can kinda see their point. I think however its on an individual basis. Some people can get away with it, some cant.
Ive been in two bad situations where things "kicked off", once I had two blokes trying to punch hell out of each other and pulling each others face masks off in the middle of a firefight. I had to react pretty fast, and in all honesty had to be quite physical, loud and aggressive to seperate them both and most importantly stop them both losing eyes. Luckily I pulled em apart, and covered their faces whilst another marshall called a close to the game.
I have seen a few situations where players have ignored a marshall because they were young, and once or twice because they were a young girl. Funnily enough the people who were fighting and the people who wouldnt take a youngsters ruling were the same kind of fools. What would have happened, if that youngster had to seperate two rugby players determined to beat each others heads in?
This sucks, and as someone said, its always idiots, that have a problem being told by a youngster.
However if the site has a decent allocation of marshalls of all ages and experiences, these problems are rare. I marshalled with a few sites over the years but NPF for the longest time and those guys have it right.
They do have younger marshalls but they mix the experienced and older with the younger ones. The emphasis is on teamwork, if the marshall team is tight and good, then there should be no issue if one marshall is younger, because the team can sort it out.
Anyway good luck with your exams, and dont worry too much, Im sure other sites will want keen marshalls. If not, you can only get older