If the final goal is to fly for the airlines then the route you are choosing may not be the best. Airlines tend to tag students during approved courses and also part sponsor as they get a reliable product at the end There is also the multi crew only licence. waiting and going on a course at OAT or FTE may be expensive but will probably improve employment prospects. Flying Tugs is not to be taken lightly, Insurance is expensive and not for the low hour pilots. Silver C gliding is a good experience to have to be able to know what the glider pilot wants out of the tow he is paying for.
Getting a class one medical is essential book the initial at LGW and get it done. without it you are going no where in the airlines.
My advice let him go gliding its cheap will keep him busy (gliding is cheap in cost but expensive in time).It teaches good solid flying skills and airmanship and It is a great way to network. Go for a PPL if you wish but if you go down the route of an approved course then you will not get very much if any credit for having it.
This is all from personal experience from a 13yr old glider pilot to my current position of a trainer with one of the major airlines.
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