Yes. 14 on Easyjet, 12 on Flybe. Just ignore the pop-up window if your child is actually old enough. They only put that there as a disclaimer in case your child turns out to be 13 and they reject them at teh airport.
The good thing about budget airlines is that they tend to fly into less busy regional airports which are much simpler and easier to navigate for the novice young traveller. DS managed Rennes to Southampton just fine at 12. All three older children have travelled Easyjet and Flybe alone at ages 12-15.
DS actually flew translatlantic unaccompanied (including a stopover in Toronto) at just 16 (he'd turned 16 a few days before). (I was very proud of him) But he learned how to do that by flying short-haul in Europe on Flybe and easyjet. I can't recommend enough letting them do it. (says the woman who is freaking about her daughter interrailing in Eastern Europe this summer...)
No, not a gamekeeper but links to that kind of world....
Has your DS met the family before - mine had not, and although we had seen photos, I asked them to be sure to meet him at the airport with a sign with his name on. It all worked very well and he had a great time, however he now wishes he could live in Nice/Monaco (so do I, some of the time...!) as the French family had a great villa in the hills overlooking the sea, with pool, petanque, meals on the terrace etc. I felt sorry for the poor French boy who came here - although we live in a lovely rural spot, the weather last August was cold, grey and wet when he came over - I don't think he had realised how cold an English summer can be. He did love the weekend we spent in London though, and his dad emailed me back to say he wanted to come and live in London...
I'm a bit concerned about DS on his own. The family live in Nice and are flying out to Bastia, arriving about half an hour later than he's getting there, so he'll have to wait by himself until they arrive. There are all sorts of permutations to that scenario that I don't like much!
DH has said not a good idea, and for DS to fly to Nice the day before and then go out with the family. He can then fly back by himself from Bastia.
I did eventually get hold of Easyjet, and he's fine to fly and be booked in as an adult - you are right.
My DS did this last year, aged 15, flew from Stanstead to Nice on Easyjet. I don't remember having any problems booking him on to the flight (maybe I just put him down as an adult?). I did send with him a letter signed by me and DH giving him permission to travel and quoting the name and address of the family he was going to stay with. Their son, also aged 15, then flew back to UK with my DS. It was all fine, even though my DS had a bit of a panic when Stansted got evacuated due to a security scare just as he was waiting to board, everyone had to go outside and then they all had to go through security all over again once they were let back in and he was worried he would miss his flight because the queues were huge.