Try this experiment

Create a very good player with low current ability (Maybe 60-90) make him 14, dump him in some crappy league and see what happens to him.(You cant sign him)

Had a stiker in the Nigerian league..left Left Nigeria for France at 18 to play for some french 2nd division team and a year later he was bought by barcalona.. ended up meeting him in the champions league final but thankfully won

I edited a database in FM09 an added a 'Tyoldinho' (my Brazilian alter ego ) into the Sao Paulo team with 85 CA and 200 PA.

With high hidden attributes and Determination, he improved quickly, was snapped up by Ajax 2-3 seasons in, then Man United bought him for somewhat £12m, played him first team football for 4 seasons and then the famous Tyoldinho (top goalscorer in EPL twice) was signed by Barcelona for £58.75m rising to £60m after such and such appearances. Made 30+ Brazil caps before I got bored of the saves and was brilliant!

Note: I also didn't sign him or do anything to alter his journey in life I just played the save as a normal save game, and checked up on him regularly!