"Grooming" or even encouraging can be a rollercoaster. During a time when women weren't allowed to attend SAs, my mother suggested I consider it. I mentioned that women couldn't attend, but she (wisely) said, "They will one day." By the time women were admitted, I had rebelled at the thought; NO WAY did I want to attend a SA. This happened in part b/c I thought she was pushing me, when in fact, she was simply making me aware.
Memorial Day WE of my junior year in h.s., the first class of women graduated. I watched it and said, "I could do that. I WANT to do that." After that, it was entirely my decision. I'm not sure either of my parents was all that excited about their only DD attending a military academy. But they realized it was now MY dream and supported it.
Kids who will be successful at getting into a SA and successful at a SA will naturally do the "right" things in h.s. You can't force a kid to like STEM. Maybe the kid is destined to be an opera singer or composer. You can force a kid to like sports, let alone certain sports. You can't even force a kid to lead.
IMO, it's about providing opportunities. If at all possible (realizing it's not for some), get you kid into a h.s. that offers challenging core courses in math, English, etc. Expose your kid to various sports -- hopefully, he will find one or more that he loves and support camps and tournaments as you're able, financially and time-wise. Give him the opportunity to join clubs or participate in other activities (e.g., scouting) that provide leadership positions.
A friend of mine has a really, really smart daughter (academically). She's also great at X-country. However, her passion is ballet -- and she's exceptional at it. She's actually considering postponing college to do ballet for a time. The point is that parents can provide opportunities but the kid has to embrace his/her future.