We tried doing the New Scout Patrol thing, but we found that the older Troop Guides didnt' hang with the younger Scouts enough for it to work well. Next time we have younger Scouts we'll encourage patrol formation such that it mixes them with older Scouts more. AND we'll have youth leader training within a few weeks of elections.
In my experience, this can go the other way too. It depends on what (who) you have to work with. When I was about 14 I was set up as Troop Guide for the newly bridged over guys. I had a younger brother right about their age, and I think that helped me communicate well with them. So we all got along swimmingly, I got to show off all I had learned, and show them the ropes. By the next year, I was off to be SPL and that group mostly stuck around intact. We even got a couple Eagles from them. I also inadvertantly set myself up to get voted into OA my first year of eligibility because I had a large fanbase.

However, I can also see it going the other way; I suspect it depends on the guys you have to work with.