What level are you defining as accomplishment? High school? College? Pros?
There are lots of little IT's along the way. Some parents mistake IT at an early age for their kid being bigger and stronger before other kids.
My daughter was a girly, girl until she agreed to play rec softball at age seven. She grew up to play college softball. Maybe IT was when I saw in a middle school softball game when she made a goalie save and took a rocket to the ribs on a horrible outfield to prevent a ball from getting past her in a 0-0 game. Maybe IT was after losing the middle school league championship the next year and sitting in the car with a killer look stating, "Losing $ucks." IT was more likely to be when she grew to 5'10" freshman year of high school when size and strength matched skills. She was a physical late bloomer.
With my son maybe IT was when his favorite toy was his Little Tikes tee ball set from the time he could stand up and swing. He dragged it out to the yard every day. Maybe IT was when others humored me in his preteen years when parents would tell me I didn't need to save for college because of sports (very humorous). Maybe IT was in LL when he shook off a horrible day with, "I don't suck. I just didn't play well today." Maybe IT was when he was fifteen and played in an 18/19U tournament with a bunch of players headed for college ball and held his own.
But here's the moment I was sure. Both of them were/are multisport athletes in high school. They had/have the opportunity to play two college sports. The definite IT moment as when they called themselves softball/baseball players first.
I figured my kids would get as far as high school sports if they wanted it. Both parents played college sports. The question was would they want to be college athletes? Would they do the work. Would they understand the sacrifices to get there (social life, work ethic away from the team)? They both wanted/want it badly. My kids wouldn't/won't drink soda in high school because they think it's bad for their bodies relative to being an athlete. That's discipline. The discipline to want IT is IT.