To answer the OP's question, a draft eligible sophomore is still at least 21, the same as most juniors. That being said, the several draft eligible sophomores that I know that were drafted, did wait it out another year, and did very well. If he is drafted higher the next year, as a junior, will depend on how well he plays his junior year
If this is general question, ok. If it is pertaining to someone you know, hopefully they have been approached by scouts and possibly advisors if they are being considered for this year's draft. If the player is a possible 1-5+ rounder, an advisor costs nothing at the moment. You don't contact advisors....they contact you.
A senior sign with a bonus "that wouldn't even buy a RT plane ticket at today's prices" got the call up several weeks ago. It happens and everyone is rooting for him!
On the Baseball Reference site, there is a column that indicates the "age" of the player in relation to the average of the other players at that level. You probably want to be a "-" rather than a "+" at any level.