By doing that you just end up in an ever increasing cycle of dripped up cars.
If you are financing, buy a nearly new one, pay for it then build from there.
The problem is, he's never going to be able to pay it off
OP, this forum has a bad reputation for turning everything into financial advice - normally I'm against it and I've even been on the receiving end of it a few times. But please, listen to this.
You've said 2 things that stood out to me - that you're saving for a house deposit and you're about to spend 25% of your earnings on a car loan. 25% is a lot, not when you're living at home - you might chuck another 25% into savings for the deposit, spend a few quid fuelling it and on a social life etc. You might even throw your parents a few quid for rent.
Assuming the finance is 5 years and you're planning to but your house before you turn 29, that means you're still going to be paying off the finance on the car. Your mortgage is going to be 1/4 to 1/2 your earnings, realistically. Add the car finance on and youre spending 1/2 to 3/4 of your earnings before you even start paying bills, feeding yourself etc etc. It's just not possible - unless you're earning a fortune and the 25% of your salary is over 6 months!
And trust me, in 2 years time when you have the deposit saved, you're going to reeeeally resent those loan repayments that are stopping you from making the move. And you'll be left with a 2 year old car that is worth less than the outstanding finance.
Go buy yourself a Clio 182, enjoy the car and more importantly, enjoy your life from somewhere other than behind a wheel. Save this new car obsession until you're old enough to afford it properly