I have a 3.5* OL which has capped 11 on both speed and strength which is very confusing thought is should be 17.

Physical skills cap randomly regardless of talent. You could have a 5 star talent cap at 11 speed and 8 strength.
Non physical skills cap based on talent though. At 0.5 star talent, skills like passing would cap at 11, but then you'd have a small chance to improve on them with later training up to a maximum of 3 higher than their original cap. For example, a 3 star talent would normally cap at 16 passing, but if lucky could reach 19.