I've never seen it addressed, though I'm sure it has been.
Assumedly an overwhelming proportion of the Survivor applications the casting crew recieve are from the younger age brackets, 21-25/26. Expecially "age 21" because there'd be a large # of people that have been antsy to apply but didn't meet the age restriction.

The number you hear thrown around alot is 1/38. As of late there is a 1/38 chance of getting called for a semi-final interview.
But what I figure is if you're from the early 20's age bracket the likelyhood would probably be much lower. And reversely, probably much higher if you're in your late 30s or early 40s.

I was just wondering if anyone had any insight into this, or if the casting directors do in-fact cast relatively proportionately to the applications recieved?