I've never seen it before but am always averse to providing credit card details for purposes of "age verification"...
I always treat those with suspicion. There cannot be any legal requirement for it as so many other sites (including Sharks) have happily operated for years without it.
DO NOT USE IT. They tried to charge me $48.62 even its suppose to be free trial and stuff. It was good i used prepaid card with very little money inside. They tried to charge me anyway.