i used to earn 600 pound a month and gave my mom 200 pound, yes this seemed a lot to me then and i always moaned but this included, roof over my head, electriec gas water, phone bill, internet access plus all the food.
my mom had 4 kids and a single parent so things were also tough but she had to do it. when i moaned she told me if i dont like it then i should have stayed on at college and then i wouldnt have had to pay.
you may think it is alot to ask but like me, when he moves out into his own flat or house, what will he have to pay, on my first house i had to pay each month 550 rent 110 council tax 40 gas 40 electric 40 water 30 phone bill, plus my food shopping and money to get to and from work. so just the bils were 810 without any food shopping or money to live. why dont you list all the things you pay out and show him, make him understand that you are not robbing him of his hard earned cash, life is tough and he needs to realise it while he is young.