As you probably know, if you keep them room temperature they will last about 30 days. If your 17 year old will be using that insulin within 30 days, then no worries! However, if you want to keep them refrigerated – hoping to bring unused insulin home and stick it back in the fridge, then I would bring an ice block and a small soft-sided cooler. Don’t put the pens directly against the ice blocks, of course.
If the ice blocks are frozen when you arrive at the airport and your son has his letter of medical need from the doctor (for security) then there won’t be a problem bringing it through. Have him keep that in mind when he returns, if he wants to use the ice blocks again. They must be frozen when you go through security! Otherwise they are subject to further testing and I have no idea how they do that on a closed ice block.
Does he have any FRIO packs? Look them up. They are very handy at protecting your insulin pens from extreme temperatures. It’s a misnomer that it keeps them cold. It keep them in a room temperature range – which is great if you supplies are subject to some sunshine or hot weather conditions. You simply soak the pack in water for the designated amount of time, then slip them into a sleeve with your insulin pens inside. I would try it first at home. I have oversoaked mine and couldn’t fit the pens very well inside.
Good luck to him!