I have only one grandson and he has a birthday on Christmas.
Last year I gave him an iPhone for his 14th birthday and Christmas. He was very happy and thankful.
I asked him this year and he says he already has everything.
Have suggested: camera, laptop, MP3 player, … But he says that could all be his iPhone.
Do you have an idea?
If he already has everything there's probably only something immaterial. I would go for example Very pleased about a visit to an auto show or the Mercedes-Benz Museum. Maybe there's a suitable fair / concert / museum etc.
Camera and mp3 players are already "extinct" in our generation as they have been replaced by the phone. Airpods are to be due Iphone, wireless headphones (the new future) that almost every teenager wants to have nowadays
Gaming laptop that is VR-capable
and next year
a VR glasses (such as an Ocolus rift s)
He'll probably wonder why you know what's currently in.