Is there a general rule of thumb on a young prospects age/ratings determing which level of the Minors they should play at?

For instance, I have 20 year old 63 ovr SP (proj to be 73) in LoA, where he's been for the past two seasons. I should move him up to at least HiA, correct? He's only 20 and certainly has much more developing to do. What happened if I bumped him all the way up to AAA , skipping Hi A and AA ball?

Will prospects progress equally (depending on coaches obviously) regardless of what level they're at? Thanks in advance. I just took over this team and see some okay prospects scattered all around my minor league system, just looking for some insight on the best place to play them so they'll progress.

Progress depends on coaching, playing time, a little bit on success, and how far away they are from their projections.  They can also receive promotion bumps.

My opinion...

I typically start 18/19 y/o out in rookie or LoA, depending on when I acquire them.  20 is typically LoA/HiA, 21 -- Hi-A/AA, 22 -- AA.  If they're future major leaguers, they should never spend more than 1 season per level.  And I treat Lo-A and Hi-A as 1 level, so my guys typically spend 1/2 a year at each.

If he's going to make the majors, I'd put your 20 y/o in Hi-A this year, AA next year, AAA the next, then ML when he's 23.

He should be in AAA when he has to be protected on the 40.   How you get there is largely irrelevant as long as you're not keeping him at one level for more than a season and a half. 

Since he's been at Low A for 2 straight seasons, I'd be concerned about the guy retiring if you don't promote him soon.  I realize he's still only 20, but retirement is still a real possibility if he doesn't feel he's going to get a chance to show his stuff at a higher level.

I put my best prospects where my best minor league coaches are. Generally I start a guy in LoA or HiA, and bump him up to AA the next year (assuming that coach is decent) and AAA the third. I have no problem with a guy spending one year in A-ball, half a season in AA and 2 and a half seasons in AAA if my coach at that level is really good and the AA coach sucks.

What about ML developement? Assuming the player is in the bigs by 23, will that stunt his final growth or will he continue to develope at the ML level?

Players tend to get about 97% of their development during their first four seasons, regardless of their ages or where they are playing.  What will stunt their growth during those first four seasons is not playing them every possible inning they can play and putting them under bad coaches with terrible patience ratings.

He will continue to develop regardless of whether he is at the ML level or not.  Players know if they are playing and if they have been in one spot for too long, but they dont know what that spot is.  Hard to explain, smoking Peyote helps.