I did some tests in the past
http://www.shrapnelcommunity.com/thr...b=5&o=&fpart=1
To make it short, the old age threshold didn't help anything to prevent afflictions. Kristoffer agreed this is a bug but i didn't find a fix in 3.06.
The only big help i found was growth 3 scale. It helps really to prevent afflictions at all. I had the feeling especially disease wasn't much present.