Each player has a potential cap, in your case it is for all star potential. You are quite likely to reached that limit now as your salary before this season was that high. When that happens your player starts to train much slower and I actually have no good guess how much slower but logically it will take at least 2-3 times longer to have pops in a skill.
See this thread
(98371.35) for a good estimated value for the salary cap for a player. All-star cap is somewhere between 40-65000 and that is probably where your players salary are right now if you added 3-4 pops this season in a skill that is a primary skill for your player.
Should also be noted that it is not unlogical that it takes a little more than 4 weeks for a 23 year old player to pop in outside defense, especially as the player already is 23 years old, at least if you are training two positions (my guess is that you are combining PG/SG).
Hope this answer clear things for you. And by the way, this should be posted in the question forum and especially not in this thread.