I think it depends on the dealer's "policy" most of the time but they will fall back on the insurance argument if they don't want to let you out on their bikes. One dealer in my area wants age 21, 2 years driving experience. Another wants age 21, 1 year experience, less than 2 speeding tickets and you leave a bike with them.
That leaves finding temporary insurance (if it's possible) or trusting you to take it out. When I was looking for my first bike I went for the area of the market were depreciation would not to effect resale value if I wanted to get rid after a few months. To be honest I wasn't expecting big things from my first bike, just wanted something to learn on before upgrading after a few years.
Turns out I got a Fazer and have no intention of selling it.....ever.