Is RPG the only genre that ages well?

Time ravages all.

" Absolutly not.  Between dated mechanics and often poor graphics in the first place, RPGS age terribly. "

Depends entirely on the game. I don't think you can point to any one genre and say hey these types of games age well.
It's all on a per game basis as well as personal bias.
Baldur's Gate series, Fallout 1,2 , Starcraft, for example if you tell me that these games have not aged well I'm liable to stab you in the eye (just one tho)
Depends entirely what the individual still finds entertaining for him/her.

RTS games age very well because not much has changed over the years.  The sprites are now polygons and the explosions full of dynamic lighting, but the game play and how everything is delivered is mostly the same.  You can go back and play Age of Empires 2 and still have a great time with it even though it's over 10 years old.  The same is true of C&C: Red Alert 2 and Starcraft.  I'm not saying there haven't been improvements.  I'm just pointing out that those changes haven't been so play altering that going back is not fun. 

Your totally right, I still play warcraft3 every now and then and its still awesome. And it came out in... 2002?

I think it speaks more to the tastes the of the players than anything else. For me, a lot of the old school RPGs are unplayable for me, but then I've never been a huge RPG fan. Hpwever, I can still put Goldeneye in my 64 and enjoy the hell out of a four player deathmatch with some people. They play way different and a lot of time the mechanics are old and weird for today's standards. It's all in how you look at it. 

I find that RPGs and Puzzle games age the best. 

Just about any game that focuses on graphics will not age well (FPS are a good example). I think a lot of SNES games hold up great because for the most part, those games focused on gameplay and didn't worry too much about graphics. The DS is very comparable to the SNES as far as graphics and controls (if you don't count the stylus controls), so if you like DS games a lot of the classic SNES games hold up great (Link to the Past, Chrono Trigger, Super Metroid, Super Mario World). 
 
I think where RPGs don't always hold up is when their gameplay mechanics don't hold up to todays standard (ie, no auto-save, required grinding just to progress in the game, etc). I tried playing FF4 for the DS a little while ago and granted, I've never been a big RPG guy but I found it to be nearly unplayable. Sometimes there's a reason they don't make games like that anymore.
 
Also, I think you can't really say a game "ages well" if you've played it in it's day. It's easy to say FFVII holds up well if you remember playing it back in the day because the graphics and gameplay differences are more acceptable to you, plus there's the nostalgia factor. For me, I'd say a game "ages well" if someone who never played it when it first came out but tries playing it now and they think it's still good. For example, I think the old Zelda games hold up awesome, but a friend of mine who never played the old "top-down" Zelda games (only played from Ocarina and on) tried them and hated them.
 
The downside of the switch from 2D graphics and sprites to 3D polygonal graphics I think is that 3D graphics don't age nearly as well. Once the graphics improve over a couple of years, it's really hard to go back. Just try playing Metal Gear Solid for the PS1 now. Or better yet, don't - it might ruin your fond memories of that game.
 
EDIT: I just wanted to add that I think RPG is too broad of a statement to say they hold up well. To say that, you're implying that someone who likes modern RPGs (ie, Mass Effect, Fallout 3, etc) would like old RPGs (Chrono Trigger, FF3/6, etc.) I mean, you can't even say that if you liked Fallout 3 that you'd like Fallout 2 because the RPG genre has changed SO much since then. If you specify JRPGs, maybe, because they haven't aged or progressed as much, which is why I can't stand them now, even though some of my favorite old games are JRPGs (Chrono Trigger, FF3/6, Secret of Mana).