You might well be an exception (being an FT'er and all..)... but drivers under 25 have a shockingly high average accident rate.... to quote Driver Education Australia..

"drivers aged 18-25 represent 13% of all licensed drivers but account for 27% of the states road toll.... This group of drivers (under 25) are twice as likely to die on our roads" I bet the statistics are similar over there....

One can hardly blame car rental firms for building that into their fees & charges.

If you currently have comprehensive insurance on a car you own you will be paying more for that cover than a 40 year old would for the same vehicle... for those same reasons.. That is how insurance works... It is not "exploitation", it is realistic risk assesment.

Being the cynic that I am however I suspect these rental underage fees are in fact so high because they are not actually aimed at "coverage" (although such arguments are valid) but at pushing under 25's away.... I suspect they don't want the business... or risk.