Whether you like it or not, it’s human nature to be competitive. It’s just your choice whether you want to be assertive about it or not. At the end of the day however, it will always be something that would trouble you unconsciously.
People like to belong. Especially with what people in your age group are supposed to be doing. So naturally, if a person you thought would always fall behind you suddenly is ahead of you, you’d be bothered and feel challenged to overtake him/her.
It’s the human psychology of competition. Because everything about life is. You need to beat others to be on top. You need to beat others to survive.