The Imperian mentor system seems arbitrarily restrictive - I started this game entirely new to Imperian and by the time I wanted a mentor, I was technically "ineligible" for the the system. Despite this, Ahkan has always been super nice to me, and his help is a HUGE factor in why I've bought credits/lesson package/subscription - it's a real shame that he can't get a bit of payback for his extensive time and effort, simply because I leveled out of the mentoring bracket before he found me.
Please consider adjusting the mentor program. In other IREs there isn't this restrictive level requirement, and people are able to swap mentors.Furthermore, the IRE-wide 3-purchase limit seems pretty unfair, as newbs are likely to start out purchasing small, before graduating into bigger purchases. This only invites metagaming for big buys - just let mentors always get credits. It encourages that relationship and discourages the cheesy mentor juggling most players do when making big buys. If someone is about to make a big purchase, their mentor really does deserve a kickback, regardless of the amount of time they've been playing.
Edit, for reference: I've subscribed for several months, bought both lesson packages, and bought straight credits. All of these are directly because of Ahkan mentoring me, even if it wasn't official.