It's really well written and makes good sense. I can't help but think that it's a little boring for them to age in exactly the same way as humans, though. Makes them less distinct.
Maybe instead of just becoming mentally slower, they also become more eccentric. The last years of an IPC's life might be filled with behavioral peculiarities like a hateful aversion to silverware, an incorrect account of past history in which all significant figures were IPCs, germaphobia, etc. Little quirks that are only tolerated on Nanotrasen science vessels because by the time an IPC is that old (s)he has probably picked up a buttload of very useful skills.