Reaching middle age is a gift, though i look at my dad and i realize it takes only a few years to make 60years of age. We never used to interact, guess i wasted sometime somewhere. I believe aging becomes faster (not really but people's feeling about it)from about 33 years.
It speeds up the further from the starting point based on percentage. 1 year to a 10 year old is 10% of a lifetime, 1 year to a 100 yr old is only 1%. The mind plays tricks which makes time relative. The feel of the body is another thing ;)