i think its judge each case on merit, you can have both young and old 31 year olds, depending on how many injuries they have had etc..
but i expeect the caution is when you get to 31 - 32, within the space of an off season and 1 or 2 injuries you can go from an elite player to just another average first grader.
and with a price tag associated with farah it can be determined as a gamble if you will get return on investment.
Still not sure age is a factor in this? A bad enough injury can end or hamper your career period. Stanley bros, Matty Head etc all had their career derailed whilst in their 20's.
Brent Tate, Andrew Johns and Darren Lockyer all came back from ACL tears late in their careers... Ben Ross even came back from a broken neck!
On the flip side we are getting much better value for money out of a 30yo Benji (injury wise) than what the Tigers did early in his career. Same could even be said for Sonny Bill Williams who spent a lot of time on the sidelines early on due to knee and foot injuries.
Regardless of age Farah is the best available option in a position we're not particularly strong in FACT.
Straight Shooter