Some doubts about high notes, is there any way I can reach them?

Hey,

I'm 15 and I have a pretty deep voice. I think I'm a baritone but
without much training. I can sing low and middle notes easily but
whenever they get too high I just can't reach them, or well I can but
just using my throat at 100% which always ends up sore, and singing
pretty off-key.

However, I've heard many male singers (like Brendon Urie from Panic at
the DIsco) with VERY deep voices, but they somehow manage to sing high
notes perfectly. (Like in this
song.http://www.youtube.com/watch?v=Y__SOBeqijg)

So I was wondering, can they really reach those notes or they're just
very good at falsetto? Will my voice ever adjust to singing higher
notes without sounding off key? I'm not saying I think I can become a
tenor but I'm wondering If there's any way I can manage to sing higher
notes like Brendon. That would be really cool.

Thanks for helping!