I don't know how much exp it takes to level from 60-61, but I do know that on my 51 shaman that I'm getting 200exp at the absolute MAX in AV, so thats a helluva lot of AV's before you'd ding
it will take a good while, but if youre really serious about staying at 60, then dont do av dailies, take every route that is furthest away from npcs as possible, and stay where enemies will have to cross so you can farm em out and take no exp.
You actually can get a bit of XP in AV. My mage solo killed the 4 guards at a flag and got 618XP rested for each. Killed a commander and got like 2k+ XP rested. It adds up if you are on offense. When the raid kills an NPC a ways away from me, I get around 18XP rested. I've gone up 20k XP with the mage with maybe 75 AVs. But now I am hanging back more. Only at 185k of 290k though.
maybe you should consider twinking out at 59 first. you can do 50-59 AB/WSG, and do 51-60 AV with very little stat differential from 60 AV. also, you can play more AVs this way.