Wouldn't it have been wonderful if Sherlock Holmes hadn't have aged. That his critical faculties had remained the same at 80 as they had been at 50.
That is what the book Ending Aging by Aubrey De Grey says could happen. By utilising rejuvenation techniques, applied routinely, the damage caused by ageing could be repeatedly repaired meaning that an 80, 120 ... or 1000 year old could have the mental and physical capabilities of a 40 year old!
For more about this seemingly incredible idea, search for Strategies for Engineered Negligible Senescence - SENS in this blog or read Ending Aging by Aubrey de Grey.