I've been pondering the books for life extension/immortality effects (quite boring and predictable, yet it's still a thing : P) and I though that, although most immortality paths are quite interesting (Elixir, Living Ghost, Becoming, etc.) they all rely on becoming a magical creature. The concept itself is quite interesting, but for RP purposes I was looking for something less magical, something that would not render you invulnerable to Warp and still allow you to become very old.
I've been reading about Longevity Rituals breaking the limit of 400+ years with specialist magi, but my idea was related to something I read about the founders. According to canon, Guorna the Fetid was at one point developing a wicked ritual to consume his apprentices to fuel her immortality. This is quite a typical cliche of evil mages in high fantasy, yet I haven't seen anything like that so far. The idea is the following: Would it be possible to devise some kind of Corpus ritual (probably Perdo with Creo requisite, or the other way around) to drain life force from a living entity (not created with magic, obviously) and improve the ageing roll the same way the longevity ritual does, maybe even adding them together? It would not be too game-breaking for several reasons, namely the fact that Warp is still an issue and that using blatant necromancy against mundanes could be considered rather unorthodox by many tribunals. Still, the concept might be interesting for characters focusing on Necromancy and still willing to prolong their lives by any means necessary, and maybe even retreating to a remote place to avoid the dangers of being exposed to warping effects.
None of the limits of magic would be broken (age is halted, in the same fashion as the Longevity Ritual), it could potentially have some drawbacks aside from the moral and legal issues (the most obvious one, eventually creating an Infernal Aura for committing a deadly sin, performing an atrocious ritual that would probably attract infernal creatures and demons) and it could provide for several story hooks for a game. There are some cool concepts in Mysteries Revised (Spell binding, using spirits to fuel things, the Living corpse itself), but none of them cover a mortal magi fuelling his own life prolonging rituals with the vitality of others (or I haven't read them! Let me know of any books/sources I might be missing!).
I haven't designed any spell/ritual yet (ideas are welcome!), but some ideas I have been working with include having to put the living subject in your lab and cast the spell during the season you're going to create your ritual (thus making your lab eventually a place with an infernal aura, quite a drawback) and/or making the Longevity Ritual have side effects (affecting social skills and/or attributes through physical and/or spiritual degradation), among others.