SrCuervo
Life hack of your cheat: The changeling Titans in their immortal form are technically immortal in age, as well as having high strength and large size. Technically, if your Susano takes years off life and can only be used on your body, Couldn't you try to become a shapeshifting titan, so that when you become a titan, you use your Susano on your titan body? It would be something like in Naruto when covering Kurama with the Susano armor, And being a titan you would not lose any life, in that state your life will be almost infinite.
I think there's bit too many restrictions. Sure, I agree on susanoo part, but others? He doesn't have ackerman benefits, he doesn't even seem to be able to train chakra as he wants etc. It's bit too nerfed. At very least he should be able to train chakra like people in Naruto so he can at least get to somewhere between Chunin and Jonin in future.
Mangekyou Sharingan is too strong for the realm of AOT so it's restricted so it's ok, giving little chakra control and the hero restraining himself by only strengthening his body with low perspective is ok with that too. It's absurd to have the Ackerman feature completely taken away, and it's not enough that even his past memories are too few 😔. You took the memories for the continuation of the story or the system made it ok but I hope you don't reduce the personality and intelligence of the protagonist.