eli5 why is there an M and A rating for games like M is 17+ and A is 18+ but both are the same. what is the difference and why are some games M and some A rated

Question

please explain how does a game go from m to a both have violence and sexual content

In: Other

Answer 1

I was always under the impression that M and R were “We advise this to be for an adult, but an adult can get it/bring in their close to 17 year old kid.” 

Was that ever real or did it just change?