We managed to give £30k to ds on his 18th. We have told him it is his money to spend on sex, drugs and rock n roll, but it would be wise to keep towards a house deposit (unless he wants to live with mummy and daddy forever), and to work/save for day to day things like car costs, holidays etc instead which he had taken onboard so far.
He is at uni (Scotland, free tuition, living at home/free commuting, working PT), doesn't need a maintenance loan so far and not incurring student debt which he knows is an extremely lucky position to be in compared to his rUK peers. We house/feed him, and agreed to pay for car insurance (currently £800/year) during uni as our uni contributions, we give him cash for each xmas/birthday, but otherwise his PT work pays for his clothes, fuel, phone, gym, socialising etc and he saves for the cheap holidays he has with uni friends.
He plans to feed the £30k into a LISA over the 5 years of uni so he will have another £5k + any interest. We are also adding bits to it when we can (but prioritising our own retirement now!), so expect when he finishes uni at 23 he will have somewhere between £40-50k as a start towards a house deposit.
If you can afford it starting saving young does add up. I put just £20/month into my great nieces bank account, + £50 at Christmas /birthdays (I get her just a small token present such as a book as she gets too much a lot from nieces friends) and that will boost her savings by £6k + interest by the time she is 18.