As far as I understood, Tatsuyas Regrowth is only limited by him only being able to view the Past 24 Hours of the Eidos. Thus he could simply Memorize the Eidos of anyone at a certain Point and (due to him having a nearly Perfect Memory as described when he memorized Tuman Bomba) rewind them to this Point.
Should there be another factor that Limits the rewind time, he could simply use it every 24 Hours to rewind himself and others he wishes back 24 Hours. This would at least significantly slow the aging to near eternal Life, if not killed.