I'm a older player that only started playing due to a younger son playing and thought I'd play just so he could practice with me and then found, to my surprise, that there were players as old as me and my son was the only player under 18 at our first Indy GT. But my 15 year old son is quite good, especially given that he's only been playing WHFB for one year and LOTR/WOTR for two years. In our area, there is a group of older and very experienced players, but my son goes toe to toe with them (including beating a top ranked US players occassionally) and he almost won the recent local one-day tourney but for a whiff on a critical combat roll in the final round game costing him the win. So, I'd never take age as a basis for judging ability, nor do I care that much about that since everyone should be given respect (besides you never know how that person might develop if given a chance).
What I ran into at a recent tourney of experienced/ranked player was a player in the last round (third of three rounds) thinking that he should beat me just because I've only been playing for less than a year and only been playing competitive for six months and he'd been playing for almost 20 years or something. He was insulting and bullying and stretching the rules throughout the match because I managed to tie him up and out-maneuver him (even though he had a maxed out Slann and two EOTGs) a few times. We drew on victory points but I won the objective by outplaying him in turns five and six for a 7 points to 3 points win (last round had 4 pts for objective, 3 for tie, 1 for loss and 5 for win). I wrote a letter to the tourney organizer describing what happened and left it at that and swore I'd just never play that person unless I had to. Even when I was much younger, I had no problem telling someone that they're being a jerk and a poor sport.