She started with her first boyfriend (and future husband) when he talked her into having a MFM threesome with a good friend of his.  His friend and he were both 20 and she was 16.  
She said she doesn’t understand why her man would want her to be with a bigger and better lover, and I said that was the whole point of sharing her, to give her a better experience. 
She has been with over 100-men and now has no interest in sharing any longer. We still fantasize and role play, but it might never happen for us.