I tested Polly when she hit 7U. Test for both IAA and Acro. Same lab, for me Michigan State. But might as well get them both as long as you're sending in a sample.
Note: I'm not advocating what you should do. Just saying what we did.
I think most people around here recommend that you test once you get to 6U.
I think that we were at 9 u when we tested. Luckily, we have not had to go much higher at this point.
Good luck if you decide to test for acromegaly, I hope you don't get the diagnosis but should Hyde prove positive, there is a wealth of experienced members here that will help and guide you with your choices. My vet knows nothing about acro so I rely 100% for advice here, I don't know what would have become of Crystal without this forum.