I was not aware he was older than Mia. Mabel would have been conceived in the December of 2018. If Mia was 16 in the October of 2018, he would not have been breaking the law.
If he is 21 now, then he must have been 19 at the time of conception unless he has only turned 21 within the last few weeks.
However, it does not sit right with me that an 18/19 year old was sleeping with a 16 (potentially 15 year old - depending on when they actually started sleeping together). 18 year olds and 16 year olds have significantly different interests and experiences. Mia was at school and this boy had been out of school for 2 years or more. It is not okay, and Victoria should have been monitoring who Mia was dating at the time.
He should not have wanted to be friends with Beth either, who was literally, in the boys own words,13/14 years old at the time.
Edit Mia said that she got with Mabel's dad in the end of October 2018 in her 16 and pregnant announcement video. If that is the truth he wouldn't have been breaking the law. It is still concerning though.