He is literally saying 'You're too young, I thought you were older
(you even perhaps told me you were 'You led me to believe you're old enough to give me love and now it hurts to know the truth!')
and now I know you aren't, get out of my mind and go home to your Mum.
Other than perhaps the lyric 'get out of here before I have the time to change my mind/I'm afraid we'll go too far' being nebulously dubious (which I don't think is too problematic given he is literally saying 'Go away I don't want anything wrong to happen/I'm not comfortable with this situation so leave!' I don't see anything wrong with this song.
It's a good message arguably 'Guys, we can't mess around with young girls' in an era where plenty did (I know they still do but we have moved on from it being sometimes seen as okay).