As a 22 min 5k runner in 8th grade I wore split shorts because they were the team issued uniform.
Started out wearing them with knee length compression shorts and a short sleeve t-shirt under my singlet because I wasn't comfortable showing that much skin. I gradually became more comfortable with the runners attire and dropped the short sleeve t-shirt and by seasons end I dropped the compression shorts too. My time dropped to 19:30 which I mainly attribute to wearing less clothing.
Broke my arm so I didn't get to race track but I was sold and next year in 9th grade XC I bought my own pair of split shorts to wear to practice.
Just Do It.