[MR4D]

That's not quite true. For instance, life insurance takes a varying times for it to kick in (varies depending on type and amount, as well as which state's laws apply.)

It's quite possible that your health insurance could be limited at first, and grows to cover more things and higher dollar amounts.

And before anyone says you can't do this, go look at your dental insurance. Odds are that your coverage increases each year so long as you have two checkups annually and don't let a lapse of insurance occur.

Note that as the ACA is __currently__ written, the situation the OP states probably exists.

[dlp211]

And what happens when you're 18 and get cancer? Building up may work for dental because even in the most catastrophic case, the costs have a ceiling, but your overall health doesn't have these kinds of ceilings. Also, every dental plan I have ever had has lifetime maximums, something else that doesn't work with health insurance.

[mikeash]

I've never heard of anyone getting hit with a million-dollar bill for dental work, so I don't think that's quite the existence proof you want it to be.