Huge age gap, should I say something?

It's recently been brought to my attention that a girl I know who is 16 is dating a 28 year old man. Now I have no problem with age gaps, I'm 17 and My SO just turned 21 but in my state it's legal. But 16 And 28 are such extremely different stages of life she's in high school and this man is almost 30. I don't want to seem judgemental but I find it hard to believe a 16 year old girl could be happy with a 28 year old man and I don't think it's healthy for her. Should I tell her mom or is that not my place?