The first decision is whether to wet shave or electric shave.
Wet shave.
Takes a bit of time to do, and can make a mess!
Cheapo disposable razors, (i.e.Bic) and a basic foam, gel or cream. Not a bad way to start, but might get the odd nick on his face as his technique improves
Mid to high range disposable like Harrys, Gillette etc, but be aware of the replacement blade cost, as it can be quite high on some brands.
"Traditional" safety razor, EG. Merkur, which use safety razor blades, that are very cheap. i.e. 5p. (Not recommended for beginners, as some technique is needed, so as to not look like an extra from Peaky Blinders)
Electric Shave
Usually quicker, some models shed less debris, less skill needed.
Basic models like the Philips One, is a good place to start, although they tend to make quite a mess with clippings all over the sink and floor and may be more suited to styling than a basic shaver.
There are many other models from £20 to hundreds of pounds, I find the Philips Rotary ones to work really well and don't make a huge mess, (there was a basic one on offer in Lidl this week £25), or Amazon Philips 3000X. £45.
Or Philips 5000 which can be used with the excellent Cleaning Pod
I would only recommend rechargeable razors, fixed cables or batteries are a pain.
In summary, I would probably start him with some medium priced Harry razors, and consider an electric one for a Christmas / birthday etc.
P.S. Some teenagers may be sensitive to being told to shave off the "bum fluff" that they have spent 15 years growing, so treat carefully!