Actually, Nature increases old age by 25 years.
See this thread:
http://www.shrapnelcommunity.com/thr...&Number=475862
for some analysis on various mages. The first two-three tests were done under non-common conditions (Burden of Time instead of normally passing time). Maxage (the start of old age) is supposed to affect the chance of getting afflictions from old age. Maxages lower than 50 do get more afflictions, but it seems maxages above 50 have little effect on the amount of afflictions.