It is rare but people in their 30's and I would still think that people think that a fairly young age.

http://www.mentalhealth.com/mag1/p5m-alz1.html

"Onset in the most severe form associated with the new gene can appear as early as age 30."

On from the original quote...Alzheimer's disease, which occur late in life. 
I would not consider 30 late in life, nor would a lot of other people. We are not living in medieval times because then 30 would be regarded as late in life.

Cheers,