You are young enough that you could eventually develop an enormous aerobic base if you train correctly. Emphasis on correctly, not necessarily "hard enough", because the biggest thing that ruins endurance athletes is trying force too much too soon and burning out. Correct training takes place over years, not weeks or months. This involves putting in a lot of time running/biking/paddling slower than you think you need to be going, with little bits of faster stuff once in a while to push your speed. This book is mainly geared towards mountain runners and skimo athletes, but the science and training principles that it gets into can be applied to any endurance athlete with huge success, since it relies on the core principles of how aerobic fitness is developed: Training for the Uphill Athlete, by Steve House, Scott Johnston, and Kilian Jornet. These are famous names in the ultra endurance world for a reason, highly recommend. https://www.amazon.com/dp/B07VN6HGZG/ref=cm_sw_r_cp_apa_khcyFbVNRDJTH