I’d most likely have wasted it. Hopefully I’d have managed a few amazing holidays and maybe learned to drive, but my friends and I would have blown through so much without a thought. My Mum grew up extremely poor and would have encouraged me to enjoy it I expect. My Dad may have stepped in to try and salvage some.
Realistically, if it hadn’t gone by the time I turned 18, I’m sure the horrible boyfriend I had throughout the end of my teens and early twenties would have spent it.