I'd much rather live a full life in 70 years than 130 years of doing nothing. And on the aging brain situation, that is plainly untrue. There is no definite causal relationship between age and decline of IQ, after a certain age the brain is more susceptible to losing memories and general senility, but those are mostly people who work in professions where their brain is in constant use will be able to from new information and memories in their brain until the day they die. The decline of physical abilities would be better attributed to why an old person can't learn guitar quickly, or that they simply have no will to. If they didn't pick up a guitar in 70 years, why start now?