Kingston
Canadian Royalty
And willingness to be on the show in the first place. When I was in my early 20's I would have jumped at the opportunity to be on the show if it was possible but as I got older I started to question whether I really wanted to be exposed like that.I once worked out that the average age of the HMs during Ten's run got progressively lower every season until the final year where it increased slightly (dragged up by the inclusion of Terri and Terence).
Personally I'd rather watch a range of 20 and 30-somethings plus a few in their 40s. The problem is it gets a bit harder to cast 30s/40s/+ due to work commitments, family, etc.