I'm sure I've already more than once mentioned my hack for againg, giving DMs based on the standard numerical DM ranges for SOC and TL. TL15 Duke, DM+6, TL0 slave, DM-6. Still has an effective DM-1 for every term (really potentially starting with Term 0, except you can't flub that without negative DMs).
The main problem with my hack is that if the ageing rate actually slows, you shouldn't be doing it every four years, regardless of DMs or start age, you either have to move to less frequent checks, or mess with the term DM as well (unless the effect of high tech health care keeps you healthy to a certain point, but doesn't actually increase lifespan, so when first roll starts at a later date (Sigtrygg's suggestion) then you start to fall off a cliff.
In a society where people have lifespans well over 100, then the rate of checks is going to have to slow down (or get even more +DMs), but that makes the whole thing more complex and eventually decouples it from terms.