It is a rebate. You have to fill out a form and send it back in order to get the credit. It is not a coupon. If they advertised it as a coupon people wouldn't get they had to fill out a form and send it in.
And I don't buy the age excuse at all. All stores have tiny print. Half the ads show on TV have it too. There are some basics you need to understand to shop at any place, and reading is one of them (unless you are fortunate to run into braille someplace).
To paraphrase: Ignorance of the rule doesn't excuse you from following the rule.
Any rebate I've ever submitted was received back in the form or a check or gift card to me so cash that I can spend or not spend anywhere I choose. That is what I consider a rebate to be. Your definition may vary.