I started seen this guy from school,he's great and doesn't push me into anything,he met my mam first(parents arnt togeher) and I told her he was 24,she had no problem with this,he showed me huge respest and looked after me,brough me home from school when I was sick,which was a huge thing. Im 18,but I don't act it,I'm responcible and vary mature I don't drink or smoke or do drugs,I look after my bro and sis.My mam told me to lie to my dad about his age as I'm his only child,his little girl! I did but now where together,I feel so bad having lied to him.but I knew he would not have even given my boyfriend the chance to prove himself.My dad now really like him but I still have to tell him the truth,I don't know how
Where going to do it together
Any sugestions how?

Your boyfriend has had a chance to prove himself, and now you have to prove you are an adult, and can make good decisions, and stand for them. Yes do this together, as soon as possible.

Don't even mention that the lie was your moms' suggestion, just tell him you were afraid he wouldn't understand the choice his only little girl had made.

Go and be honest, the longer you wait the harder it will get

I reckon you should come clean to your dad, you say he likes your boyfriend, but try and keep your boyfriend out of it as your dad will be probably say that he wasn't "mature" enough to tell him himself,and may lose them good feelings he has towards your boyfriend, I think it was wrong for your mam to tell you to lie to be honest but you did lie but you only wanted your dad to give him a chance, so sit him down on your own and talk it out, get him really nervous like your about to tell him your pregnant or something haha and when you do tell him its just an age thing it won't seem as bad haha good luck