No. OPRewards will not sue you.
I'm sure they have terms and conditions on their website.
You are young, so a word of advice... Do not trust random websites online. If they seem too good to be true (ie offers, points, rewards) then best bet is to stay clear.
What you put online ,is then online forever.
Be extra vigilant when putting ANY details into a website. For example name, address especially! and any kind of payment details.