About the 10 years lifespan cut. Though i have just a little knowledge in biology, but I know that body cells have "age"'. Youth is when cells are the most productive in regenerating, and then they keep regenerating less and less (thats why we grow weaker as we age). So by forcing Luffy's body cell regeneration into a rapid state, Iva reduced the cell's age. Techically, I think the process will make u look older, but this is manga.
I cant wait to see how that will play out. The explanation Iva gives him kind of states that out flat, that he is loosing 10 years of life he would live from this point, not from the end of his life span. That his immune system and organs will be healing and regeneration a 1500 times faster than normal (I am roughly guessing here, assuming a year = 365 days so 10 years = 3650 days divided by 2.5 days that the process should take). It kind of makes sense, a dose of poison big enough to kill you in a day would be less effective if it was spread across ten years or 3650 days of living. Since Luffy gets rid of the poison effect after 18 hours instead of expected 58 hours, that could mean he only lost 3-4 years, than again maybe all 10 years just faster than expected.
Aside from that, it is likely that after he eats to regain strength and all the blood he lost in the process, we will end up with an physically much older looking Luffy. Even if its only 3-4 years of aging then he will be in Zorro or Aces age range now, along with physically bigger and stronger body. If Luffy ends up looking the same, how will we be shown that he actually paid the 4 or 10 years of his life for this healing process?