Dating older senior
Maybe go out on a lunch date or picnic, something nice that says, "I love you, so let's talk and spend some time together." She may not understand at her age that even a couple years can be drastic for teens in terms of mental development, maturity, experience, and what they want to spend their time doing.
Just let her know that she's in charge of herself, but as her parent, you are in charge of feeling concern and making sure she's taken care of.
If you're worried about the boy taking advantage or even just pressuring her to do anything she doesn't want to, make it very clear that you're open to any and all inquiries she may have.
Also: under any circumstances whatsoever, when it comes to her body "no" means "no", and she is in control of what she does and doesn't do - not someone else's desires/requests.
The best thing to do is show you support her but also are just worried.
It would also be a good idea to meet him, just to make sure he is a responsible young man.
You can't be there physically for her all the time, but if you can start the discussion yourself, you'll be the voice that comes to mind when she needs to recall all you've taught her. Tell her how you feel about it and what your concerns are.
You cannot make this decision for her, she will just rebel against you and continue to see him.
Their will be peer pressure on both sides so she doesn't need the stress of her parents not liking him to add on to it.
The best thing you can do in this situation is show support.
If you foster that strong relationship with your daughter she will value your opinions.
Talk to her like you would one of your friends in this situation.
My parents told me that I couldnt date a guy that was older than me and I continued to see him behind their backs.