No need to take any years off my life. Since I won't die until the age of 75, I could get worldwide fame as the invulnerable man!

In all seriousness, if I could, I'd actually even refuse the first part of the deal. The average human in Western civilisation already lives longer than 75, and in the future, will in all likelihood have even more increased lifespans. The only attractive part of the deal is immunity from accidents and terminal disease, but I'm willing to take that risk.

As for the second part, I wouldn't want to sacrifice huge portions of my life just to be good at what I could very well achieve on my own. Becoming instantly good at something will not actually mean anything. The success will not be mine, but the superior being's.