Hey, I think you need to read some basic stuff here on the forum, so many questions will be answered. There must be a "useful threads"- thread somewhere, cant find it right now (hopefully NIK helps out).
Concerning value, different players grow different, not only based on age but there is also a hidden factor. The fastest trainers are normally those with the most value (see value/wage thread). From my experience young fast trainers still grow in value after a season: losing because of age is less than the more you gain from experience points.