I think when we see the draftees come in that 18 year olds will have better potential than 19 years, on average. Not all of them, of course, but mostly. The 5 star potential kids will turn out to be 18 year olds, I'm willing to bet.
My 5 star guy turned out to be 19 (he was my 2nd preference). In fact, I'm 99% sure that my #1 preference, who was also 5 stars, turned out to be 19.
I don't think age has any impact on the scouting reports.
Run of the Mill Canadian Manager