as the previous message state it is not worth it.
even with the greatest elastic effect, a player loses around 8-10% of training speed per year.
according to community based calculations, a player of 25 years of age will train at 42% the speed of an 18 year old.
the sweetspot for training is around 22 years old if you want to just round out/complete a player when you train at 70% of the speed of an 18 year old.
furthermore, the low salay indicates that your player is not distinctive in any way in terms of total skills, so it is very probable that you will find a player with the same attributes at 22 years of age for a few hundred thousand $.
read the "guide to BB' thread on the forum