Having been a 15yo junior (that is I didn't turn 16 until after my senior year had begun) who probably threw less than 80 I've got to ask you how many 15yo juniors do you think there are? I certainly didn't get looks from scouts as a senior while kids who in 10th grade were older than me but not as good of players did. (I did get my looks from scouts later on and wasn't good enough.)
College and pro scouts certainly do take age into consideration but if a player is a bubble player relative to that level of ball due to being a year younger it isn't going to make up for the difference in performance on the field.
The pro scouts will probably make a bit more of an allowance for age but they'll also take the added risk of a younger player into consideration. Of course Delmon Young was a young player for his grade so if you've got that kind of talent it doesn't really matter.