Put the DVD's in a travel case (I wouldn't take the plastic cases for each movie) and you should be alright, assuming they're not all the same title.

I have purchased duty-free liquor and taken it through customs in my suitcase when I was under 21. It's illegal, but if anyone stops you with it, I'd use the excuse that it's a gift - I doubt anyone from customs will want to take the time or do the paperwork, then call a local police officer to write a summary citation for underage transport of alcoholic beverages.

So, yes it's illegal, but if you want to take the chance, I don't think it's very likely you'd get in a lot of trouble. Looking presentable and being polite when you clear customs wouldn't hurt, either.