Does promoting a guy advance his ratings or make it happen more quickly?

If so, how long do you keep a guy at a level to allow this to occur? I have a 19 year old at HA. My plan is to advance him to AA after 50 games and then AAA after 50 more, provided his numbers are decent.

Also, does demoting a guy, permanently or temporarily hurt ratings?

Thanks

There's no real evidence that the "promotion" cycle is anything more than a marker.    I know, if you get a "regular season" cycle and promote immediately, that you won't get a promotion cycle. 

Demotion penalties aren't automatic and, sometimes, the ratings are recovered on the next cycle(assuming the player is young enough to still be developing).   But there's really no reason to demote an important player.   Once you make the decision that he's a BL player, leave him there.  If you're not sure, don't do it. 

Mike, I understand. So in your opinion, you are better served to leave a player who is probably a backup but maybe could pinch hit or platoon until you're ready to play him every day?

When he's one of your best 25, I'd call him up.   IF he's a 4th year player on your 40.   I'd only call up 2nd-3rd year players if I were going to play them every day.   A good example is Hardball Dynasty – Fantasy Baseball Sim Games - Player Profile: Kirt Keller.   He's one of my best 25 but he would be in the 1B/DH rotation at the BL level.   I just added him to my 40 because I want him on my playoff roster to PH but, during the regular season, I'd rather have him playing every day, when he's 100%, with my best minor league hitting coach.

One thing I've noticed is that if you promote a minor leaguer at the end of the minor league season - especially if his team made the playoffs and he got a few extra games - you sometimes get another "bump" that you otherwise wouldn't have gotten. As Mike pointed out, nobody has been able to prove that this is an actual new bump that he wouldn't have gotten later anyway, but I always like to promote my minor leaguers one level at the end of the year, just in case. If nothing else, it's a nice psychological boost that makes me feel like my guys are getting better.

I do that too.   Since I don't know for sure, it can't hurt if I planned to move him up anyway.

I was reading - somewhere - that in a development chat, age of prospect vs level was discussed and it was confirmed that it's taken into consideration for development purposes.

I have a few decent prospects in HiA that are 20 year olds. Should I consider having them repeat?

I have a top prospect that is just coming through the system (spent a few Rookie games, then split Low A/Hi A), he is 23 now.  We are about to enter our ST games.  Will it help or hurt his development to come up just for ST when he is only in Hi-A?

It will definitely help.  Make sure he gets enough playing time in ST.