Only those who at Fair Isaac could accurately answer your question completely (since only they know the formula). However, we can provide some ideas for you. There does appear to be target AAoA and oldest account ages that lead to increased scores (and bucket changes). I believe one is thought to be 2 years (which you have obviously passed). The comments on your MyFico reports will provide some info. Such as high achievers typically have AAoA between 6-12 years. So a 6 year AAoA is likely another milestone. It is also mentioned that high achievers typically have established credit 19 years ago (oldest account 19+ years old).
There are likely intermediate age milestones that I am not familiar with, but others may know. I think hauling may have compiled a set of important age milestones.
Your scores are quite good for someone with a young file. Be patient and always pay on time and you will be rewarded. You may also want to read "credit scoring 101" for additional info on scoring etc.
Cheers
