Innate Attack: Aging (age)
Your attack does not inflict damage but rather ages the target directly. This could be through magical ageing, a disease or nanobots. Each point of damage ages the victim 1 year. 25 points/level
Enhancements and Limitations
Aging has an "innate" unhealing enhancement going on, but in case its not permanent: Temporary -50%: Your attack is temporary aging rather than permanent, every time the victim would heal 1 HP but is at full HP he can instead roll against his or her "Original HT" meaning that if the victim had 13 HT originally, but lost a couple to aging rolls he would still roll against 13 not his "new" HT. Success returns 1 year, Failure and Critical Failure do nothing.
Good enhancements would be Malediction to make it works like a spell. Aura to make it, well an aura of aging. Cyclic with varying durations work fantastic as well. For Limitations Resistible is basically a staple unless using Malediction. Other great limitations would be Blood and Contact Agent as well as Sense based.
I initially was costing this to be like a fatigue with a Weird +50% enhancement but the lack of instantaneous feedback stopped me from continuing on. A single fatigue attack (or any attack really) for 2d that hits an unarmored target has a decent chance of at least making them stop spending FP on extra effort if not forcing them to change tactics. An Aging attack that does 2d will age someone... 7 years on average, which on hindsight is not that much... for instant feedback. In the end the cost is as Fatigue attacks with a Weird +50% enhancment and a +100% Cosmic Unhealing modifier. Aging damage can even be scaled back from years to months, although I suggest lowering the cost to 10/level