Mecha can be any age, depends on what you do with it, you could even draw in an adult audience with it. Evangelion can be pretty messed up, especially towards the end of the series (and the movie that followed) and probably only just fits into the teen category.
I think with any show you want to direct at a teenage (or even child audience) you can make it entertaining on 2 levels, one that appeals to the age group and one that appeals to adults. A good kid's/teen TV show would be something that a parent can enjoy with them. Why do you think so many kids show are loved by people who are too old for them (Spongebob, Danger Mouse, Count Duckula, certain anime shows, even the latest My Little Pony). Okay, this is a webshow, but if there's something that'll interest older people, then it's a wider market.
I'm sure teens watching mechs will like some of the action, I mean, it's giant mechs fighting, to some people, that's pretty awesome. But as a 12-14 year old I think I could relate quite well to plot as well. I started using Dark Basic when 14 and had huge ideas of plot for my video game. So I think if you have a strong & exciting plot, with relateable (and 3 dimensional) characters then you may be on to something strong. Even for people older than 14. I think even for 12-14 you don't want too many cliches at once.
Kids don't think your guy is worthy, this would be something for him to work for, this would create a lot of conflict and offers him a journey and allows him to be 3D dimensional, he has his flaws as well as strengths which could become more apparent to him as he goes on.
Kind of like Shinji from Evangelion, who sees himself as being very weak and has a father who looks down upon him as a weakling. Also, he's seen weak by a fellow pilot. He often doubts himself a lot and has a lot of internal conflict, though from the sounds of it, you don't want to psychologically torture your protagonist (like they did with Shinji), so I wouldn't think of Shinji as a model for a character, the main different would be that he gains strength the more he fights and saves his friends and earns his respect. In finding out his parents were legends, he sees he's got to live up to their greatness and pushes him to try harder. And of course, he proves himself not to just himself, but others too. To me, this sounds like what you might be looking for in terms of a protagonist. In some respects, it is cliched, but these kind of shows can be, but I wouldn't say it's over-the-top in terms of cliches. I watch Transformers: Dark of the Moon last night, that was cliche after cliche and the characters weren't convincing either...and it was boring too.
At least that's my feedback on the little information provided about it.
But as for it being live action, I think it'd be difficult to say, there's more you can do with animation that's cheaper. I think for it to be convincing as a live action show would be expensive. I mean, stuff like Power Rangers were loved because it was so horribly cheesy, bad acted, bad writing, bad plot, bad characterisation, unconvincing set, unconvincing costume design...in fact, I can't remember anything good about that show other than the fact I loved it. But that's a pre-teen me, an age when I still believed in Santa Claus.
