I regard high senior skill on scouts as a waste. With seniors, you pretty much know what you're buying. Psychology is the only skill needed for them unless you are in the habit of buying late bloomer trainees who are blooming at 22-23 or so. Then a senior skill would be useful. But I think that’s not that common and I wouldn't plan to buy many trainees of this sort.  People who stuck to late bloomers and kept them in the team until 21-22 or so aren't very likely to suddenly sell them then, after they’ve waited so long. So supply should be very limited. Of course, it doesn't hurt to try. I prefer 18 year olds, simply because I want to train them my way and shape them the way I want to.