It’s not just age, it’s personality too. Some adults can’t be trusted with money not to drink it, inject it nor gamble it, whether 21 or 51.
Lots of youngsters would actually treat it seriously and not waste it. It’s not really good to tar all youngsters unfairly assuming they’ll spunk it away on rubbish!
Our son still has his entire (smallish) inheritance from one grandma safely in the bank continuing to earn interest. She died when he was 6 and under the will it was put into a trust bank account for him to an access at 18! Five years later, he’s now 23 and it’s still safely in a savings account as he’s ring fenced it himself to go towards a deposit for his own flat! To him, it’s sacrosanct. I’m sure he’s not alone.
MIL died recently leaving her estate between OH and his sibling equally. We’re doing a will variation so that OHs share goes to DS. It’ll set him up for life as he can use it along with his other inheritance to buy his own flat/house on probably only a 50% mortgage, so he’ll save a fortune every month in not paying rent and then he’ll have more of his wage left to actually live a life rather than paying someone else’s retirement or billionaire bankers!
Hes only 23 but has already shown he is responsible with money as he always saved some of his Xmas and birthday monies throughout his childhood years to buy something significant rather than waste it all on crap and sweets, so we have no qualms to trust him to do the right thing.
MIL just wanted everything split equally between her two kids and always said she’d leave it to them how much of their half share they’d give to the grandchildren, but there was the clear intention that the grandchildren should get more than a token/nominal amount, even when the GV were small.