Grandson 18th

It's difficult with boys I think. Money is usually welcome! An account with some money in maybe? Plus a fun small keepsake (because often boys won't want to keep keepsakes long). I did see you could get a high quality hammer with a wooden handle and their name engraved. A hammer he could use for life! Even if he's not into diy now. But - that might not be your or his thing. I would ask his parents what they think would go down well.

A quality leather hold-all/weekend bag.
You can have his initials embossed on it.
We got each of our boys one, still going strong.

For my 21st my FIL gave me 21 silver threepenny bits. I treasured them and bought more to enable me to give 18 on each of my 6 GCs birthdays.

In the old days would suggest a watch but of course they don’t wear them now. How about a piece of jewellery, I know teenage boys now wear necklaces/bracelets, or studs if his ears are pierced.

A vintage bottle of whisky. He can save it for when he retires!!!