You can generate a profit for buying young players, train and play for two seasons and sell him at 3rd year. As a player gain exp faster at a lower quality so buying young 3* isn't too bad if one only cost a token or two, and is great for subs if you play him rarely.

That is if you actually able to sell them... in my server at my level I'm unable to sell players for a long time. AI spawns being the major cultprit I believe, very few buy regular players nowadays.

On the other hand, old players usually generate a net loss but they perform better than young players with the same quality. So it's a decent choice if you are flooded with money anyway.