Ya, this is a fun question... No real right answer, its all upto your play style.
1) people say YES 65, get to 65!! dont do AA's until your 65 so you can go raiding...
- myth: people that are 65 with little to no aa's go raiding...
+fact: people looking for xp groups for 65 often ask, how may aa's/tomes you have, espically if you are dps/tank/healer (I think the only onces that get a pass on this are enchanters).
2) a few people say get a good base of aa's at 51 and exp hard at 65 for more aa's...
+fact: this works well if you are 2 boxing or have a group of friends you are leveling up with.
3) a very few people are crazy (like me) and farm the crap out of Lasanth at 55 (My Konad did 80 aa's in about 4 days of xping there, granted I spent 8 to 12 hours a day (soloing)).. Solo xps in lasanth at 55, is godly. Its truely the best thing in the game.
- myth: grouping will level you faster in lasanth at 55.
+fact: soloing with a box druid/cleric not in group but off healing you is friggin amazing (keep in mind this only works for characters that can take hits).
Bottomline: Dont let people push ya one way or the other, I did level up my rogue abit too early. I could have easyly started for until I was well in my 120ish aa's. I believe theres some points where aa's do slow down, Im not sure if its 51th aa (is a break point) and 101th aa is another.
staying at 55 to farm aa's is fun if you are twinked abit. level 59 has some very good aa's but you can buy them at 55