You know what I love about this game? NO FUCKING ASKING IF I AM 18! Like fucking seriously that gets old. You think someone who downloads one of these games doesn't know what the fuck they are doing?
Good on ya, dev!
Regarding the age verification check, I think, above all else, it's a token attempt by any responsible/sensible Developer at child protection on behalf of those parents who don't know what the **** their kids get into online and who are likely to try to sue the @$$ off anyone when they find out they've got into this.
Confirming you are 18+ is tantamount to being given a key to open the door to the novel. Some who, when you indicate you are 18+, then ask you a second time whether you are sure (that you're not telling pork pies) plan, in the event of being sued, to offer that double check as their defence in court. I believe in legal circles it's known as the Twinkey Defence.