Actually, IMHO its better to wait until you get to 60 or so before doing AAs (except maybe the RUN AA). It takes as much experience to generate 1 AA point as it does to get through level 51. So if you do AAs at level 51, each AA takes as long as completing the entire level.
AAs are also split up by character level. Basic ones are available at level 51, which are generally increased stats, health regen, run, that sort of thing. At level 55 (the next set/page of AAs) you can get more interesting ones that affect things like Mana regeneration, spell effectiveness, melee etc. The next set after that is at level 59. Each new set of AAs usually requires that you have a minimum number of AA points allocated to the previous set. e.g. you need 6 points in the level 51 AAs before you can put a point into the level 55 AAs.
If you wait until say, 60th level, one AA point is going to take WAAAY less time that it would if you did it at 51st level.
Personal preference of course, just depends if you want to stay in the low 50s game for the equivilent of (at least) 6 extra levels or in the 60s game for the equivilent of 1 level to get the same thing.