I agree with the others. You can explain your personal experiences which lead you to become a personal trainer and tell people more about yourself.
As others have suggested, put it at the 1-2 years.
I wouldn’t put more years than you have on your years of experience above, but I wouldn’t be shy in your “about me” section listing the practical experience that you have related to physical fitness. Your story might still be attractive to clients because of who you are and why you decided to be a trainer.
Just leave it at 1-2 years. In your “about me” section of your profile, you may chose to write a summation of your personal reasons for achieving your fitness certification. If you’ve been involved in fitness for many years but never got certified, let people know this. If you have achieved any special awards or accomplishments, record it in the section “awards/accomplishments”.
Hope some of this helps! I wish you the best!