When I was at level 55, I was told to wait to get aa's, but was never told why. I was getting 1 aa per Dain mission. Now at 69, I'm getting 3 aa's per mission. Is there an optimal level where you get the most aa's per mission? Thank you.

It's garbage. You don't have to wait to get aa's. The arguement is that a level makes it easier to kill mobs than "X" amount of aa's. This is true, but it doesn't take into account the speed in which you receive aa xp (outside of MM's and tasks) and once you level you get less xp (percentage)for that same mob. I PL'ed a SK from 1-75 with 450+ aa and it took 5 days of play time, while waiting until level 70 to get most of those aa's. I PL'ed a Warrior from 1-80 with 550+ aa's and it took only 3 days of play time, while stopping to gain aa's at level 51, 55, 60, 61, 65, 66, 67, 68, 69, 70....etc. Also I started a druid on another server and I solo'd from 1-70 with 350 aa's, following a similar path as my warrior, and it took about 6 days of play time....the the same feat took my main druid months of play time because I maxed out the level before gaing 98%+ of my aa's. I got similar results whether PL'ing or soloing.

Leveling makes getting aa's harder to come by, whereas aa's make gameplay alot easier, faster, more fun, and just plain better. Not to mention the xp will come faster due to shorter med times and such.

As for the Dain missions, yes they are geared more towards high 60's to 70. That is the level range where you will get the most aa's, but outside of the level ranges that certain missions have, getting aa's is much faster at lower levels.