My assumption with them being around the same age is they went through the proper channels to become Wonderbolts; like they as soon as they were old enough they applied to the academy, got in and worked themselves up in rank.



Meanwhile Dash finds herself kicking clouds in an earth pony town where her old friend lives now. I remember a popular fanon in the day was that Dash dropped out of school to stay close to Fluttershy/was kicked out. Yet she still has her dream to become a Wonderbolt. She knows if she makes a name for herself she could become a member. Seasons later, she's famous but realizes (or is told) she has to literally apply to the academy like everyone else; her fame isn't enough to cover her lack of education. Since there's so much more to it than being awesome.



So Dash reaches her dreams but nearly takes the long way around.