When my daughter first approached me about attending WP, I basically told her that I wouldn't stop her, but I also wouldn't help her. I was very conflicted because I know her potential and I wasn't sure that the Army would honor that potential. Plus, there is a huge fear factor - not hers, mine for her.
I had accompanied my 2 older sons on college visits, and getting the feel of a campus is very important. So, when she and I had the opportunity to visit WP the summer before her junior year, we went. I was hoping that she wouldn't like it, and then I wouldn't have to deal with it anymore.
Unfortunately, for me, she loved it. And we had only taken the tour - didn't even talk to anyone official.
I can't tell how far from West Point you are, but if there's any way that you and your mother can go for an orientation, it may be easier for her to accept why you want to go there. If you can't go, then definitely have them go with you to the informational meetings. The professionalism, discipline, and respect that is displayed at WP, or even at the informational meetings is just so impressive.
I also made a point of talking to other Army officers and enlisted personnel when I had the opportunity - some were recruiters at her high school and the community college where I was taking classes, but sometimes just soldiers that I met by chance. All of them told me that they wouldn't want to be doing anything else and have no regrets.
It took me a while to come to terms with her decision, but the more she was certain, the more comfortable I became with her decision. I just couldn't NOT support her with this decision, when all her life I've taught her to be independent and think for herself. Of course, she was quite happy with herself when she pointed this out to me. She basically said it was all my fault.
(All I could do was turn my face away and smile.)
Don't give up your dream, but make sure that it's really what you want. Do your research. And most especially give your mom and the rest of your family time to adjust. I imagine that today's Army is much different than the one your grandfather experienced. Maybe your grandfather needs to see a different Army experience than what he had, before he'll understand your decision.
Now I'm going to get tough. If you choose not to pursue this
only because of your family's reaction, then maybe you aren't WP and officer material after all.
Take your time, do your research and know that your family loves you and I'm pretty sure that they will continue to love you whatever profession you choose. (Remind them that you can be a doctor or lawyer in the Army. If your goal is to fly helicopters, I'd probably leave that out.) And from someone who's a little mischievous, I'd write/type/printout the Thucydides quote above and put it where you can refer to it and somewhere that your family can see it, too.
A final sidenote: My oldest son went with me to PPW. He's in his second year of a master's degree for engineering. He hadn't been very supportive of her going at all, but he was so impressed with WP, that he mentioned joining the Army to do research
And he's not easily impressed with anything.