Sure, the body reacts differently at each age, so the body of a 16 year old athlete will react differently on a training program than at a 50 years old man. Basically you are still in development, so can adapt easier, but in the same time you have to watch out more not do over-train, and not to harm your development. Consulting regularly a good sport doctor is definitely a good precaution, and necessity at any kind of diving.
As for courses, clubs, or instructors in Belgium, it is not true that there are barely none in Belgium. Belgium is a small country but has several excellent freedivers (i.e. Patrick Musimu, Fred Buyle, ...), and there are clubs, and also several instructors. There is also AIDA Belgium, so do not hesitate to contact them for an advice.
I would not advice you any training program. Generally (and especially at your age) it is not wise training freediving alone. Join a club, take a course, or find experimented buddies. There are many experienced freedivers in Belgium, so if you try, you will certainly find some willing to train with you.
Additionally, thanks to the small size of the land, you have also the possibility to take rather easily courses or join clubs in neighbour lands, like France, Netherlands, or Germany.
Some Belgium related links:
belgium @ APNEA.cz
And here, you can find some Belgian AIDA instructors (but the list is certainly not complete):
Apnea mania