Rowing is a sport which can be started in high school and even college.  Walk ons with no experience can learn the sport and within their college career could achieve expertise to allow them to compete at the highest levels.

 

http://www.thedartmouth.com/article/2016/09/walk-on-athletes-find-success-in-mens-and-womens-rowing?_h=750b5e19-25fe-44c2-8f09-c684c8992dec