One last attempt....
I imagine when your 17 your parents will help you by paying for some driving lessons.
Currently it's £22 an hour down where i live. The average amount of tuition is around 30 hrs (trust me..my Dad was a driving instructor)
You will learn a lot about the basics of of control from LFS, therefore giving you a headstart over non sim drivers, and saving you a good few lessons.
Baring in mind by the time you start driving lessons they will probably be nearer £30 an hour, investing in LFS will save your parents at least £60
That my theory anyway
If that doesn't convince them, i don't know what will.