Sorry mate, as has been said, in this current economic climate a bank won't hand out the remaining 20k to an 18 year old.
Why not just take half of that 5k your parents are willing to give, go do a PPL whilst working to save some money, then once you have your PPL and a job, do the remaining licences.
I'm afraid they simply won't give you the sort of loan you require unless you have some sort of collateral to back it up with.