First dive in doubles was at dive 19, according to my dive log (at that time pretty accurate). I was about 13 and my pops (instuctor who certified me) strapped doubled up something smaller than 80's, that felt like they outweighed me. After spending about ten minutes in the "armadillo" position I swore them off for about 10 years. I dive doubles almost exclusively know. Turns out you can stay down longer with them!