Guys like Moore, Leitch, Hutchinson, Murphy, ZFA, Murray, Carswell have played in the first team before they were 20 (and Erwin most likely would have had he not been injured). Cadden is also listed in the first team squad this season.
It's a tough call though, and I have some sympathy with the management team. On one hand, it's great to bring the youngsters in and blood them. On the other, the old "never change a winning team" mantra hangs over them every week.
I would happily sacrifice a league position or two to bring on some of the youngsters - but I'm not sure everyone would. Moreover, from a financial perspective, swapping our last 2 season's league slots for Dundee Utd's would have seen a big dent in our budget. Of course, we might have been able to sell on one or two of the youngsters, but our financial structure is such that we are unlikely to get anything similar in transfer fees - Utd spend money there we could just never afford.
Ultimately, as Melvin said earlier, we are a low risk club.