Halfords Apollo Feud Bike 26" wheels - 14" seat tube height - suit early teen

Halfords Apollo Feud Bike with 26" wheels. A sticker on the seat tube says that it's 14".  I'm not sure if this means that it's the frame size, but it's certainly not adult size. I think it's the biggest child size. The bike was used by my tallish son until he was 15, so I guess would suit an early teen.As per the photo of the handlebars, it has 18 gears.It is in good condition and there's a basic owner's handbook to go with it Collection only.