Here is my response to another posting on this subject (tailored to your son)
My daughter (almost 17) wet the bed almost to present day. We (the doctors and I) had determined that her body hasn't matured (yes even at almost 17) - she is also ADD - and was taking medications to curb her wetting (DDAVP - a medication that curbs the urge for nitetime enurisis)- I'm proud to say that she's FINALLY not wetting the bed anymore.
Now this is not to suggest that your son is ADD or anything like it.
He may just outgrow this in the years to come.
Have you consulted with your doctor to see if there maybe a medical issue with his bladder/kidneys? Ultrasounds for before and after voiding to see how much is left in his bladder? Something you may want to look into.
Here are some suggestions though that may 'curb' his urge to wet during the nite -
1- Others (in other postings on this topic for their own child) have mentioned getting one of those nighttime alarms where you insert it into his underwear (or pullup) - in my opinion - and personal life of trying this unit - it isn't worth spending that kind of money. My daughter never woke up to the alarm - only the whole house did - and getting her out of bed in the middle of the night to go to the bathroom was more of a headache than it was worth. Also - the unit 'rotted' out due to the urine - even after CLEANING it after every 'alarm'.
2 - if it is at all possible - have him go to the bathroom every 2 hours - whether he has to or not. This can get him into a routine of going. You can purchase a watch with an alarm on it and set it to go off in 2 hours and then reset it after he's gone to the bathroom. Also, while he's in the bathroom - have him sit there for at least 3-5 minutes to give his body the chance to relax and go. Let him do a puzzle or play a video game (like a gameboy) while on the toilet to let the time pass.
3 - eliminate ALL liquids and foods after dinner. If he eats, he'll be thirsty. If your son is indeed thirsty, give him enough to quench his thirst - not a full cup - but more than a sip. A bathroom sized "dixie" cup should suffice and only be filled 3/4 of the way and only filled once - just enough for a mouth full.
4- Have him go to the bathroom before bed.
5 - keep the lines of communication open. If he wets, he should be able to tell you without you getting upset/angry/distraught...etc.
6 - get a 'rubber sheet' protector for the mattress - this will be easier to clean up and save the mattress.
7 - if he wets, he needs to wash - plain and simple. I'm sure you are already doing this :) - if he's soaked through to the sheets - he needs to clean them as well (or at least strip the bed if you don't want him washing them)
Good luck - I know how you feel - I've been going through this for MANY YEARS and many mattresses later!