Lexus gave me a loaner at 20 last year. They seemed reluctant at first, but with a bit of convincing (with the arguement that I drive an IS350 (that I pay for), own a business, and am obviously mature for 20), they gave me an ES350 no problem.

As for rentals, Budget will rent at 18, as long as you call it a 'business required rental'. A few years ago I had to take my Denali to the bodyshop for a few days and told Budget that I needed a rental to continue running the business. A quick call to the company phone to comfirm that I was who I claimed to be, and they gave me a Mazda 3 (wahooooo).

Anyways, point of the story is that if you are able to convince the dealership that you are deserving of a loaner, they should have the ability to give you one.

 

Everybody quit complaining. Just because you can buy a Lexus doesn't mean they are obligated to giving you a loaner. The big difference is you are buying/leasing the car and you are paying for the insurance, whereas a loaner is Lexus' property and they have to pay for insurance. It's their call and it is not an entitlement. Don't take it personally.

In fact most rental car companies will not rent to people under the age of 25 (unless you are working for a company) nor over the age of 75. They do it for a good reason; young drivers have proportionately more accidents and once you get to 75 your reflexes slow down. It is their business and they can run it as they see fit as long as it applied equally. It's been tested in court.

 

^ Plus, as some of us pointed out, many dealerships aren't like the OP says. My Acura was under my dad's name but they never looked at my license and said 'sorry'.