My son did a year at Uni on a full loan and grant. I sent him what I could afford (not much) to top it up. When he turned 18, we lost the tax credits and child benefit for him, to the tune of £200 ish a month. Add the £50 a month I was sending him, as well as paying for train tickets back and forth, and we were considerably worse off. Obviously we offset it with slightly lower food bills. Had he stayed at uni, I would not have charged him a penny.
Having run up a massive overdraft from way too much socialising/eating out/buying crap, he decided that uni wasn't for him and dropped out. He got a job straight away on what I think is pretty good money for a 19 year old. Now he has moved home, we have also lost our council tax benefit, so we are even worse off. Damn right I am charging him rent. He has to learn that you fulfill your financial responsibilities before you have fun. Now seems as good a time as any to learn. A quarter of his wages go to his overdraft, 10% on bus fares and 10% to me. He works long hours and commutes an hour a day, so as far as I'm concerned he has plenty of money leftover for the time he has available to spend it.
Once the overdraft is paid off, that money will be going to driving lessons and then hopefully a car. He is getting a promotion in March with a pay rise, and I will be putting his rent up then as well. Still 10%, but more actual money.
I am trying to teach him delayed gratification and it is an uphill struggle. He will always be the type to spend every penny he has. I have also pointed out to him that when he eventually wants to move out, he won't have a hope in hell of finding anywhere to live round for less than 50% of his wages plus food and bills, so he is getting a pretty sweet deal. My husband and I don't live here without contributing, so I don't see why another full time working adult should either.