We stopped using a booster this past spring or early summer, so close to the same age as your DS. We've been eating dinner at the table in our sunroom most nights and never bothered bringing the booster out there, and now she probably wouldn't want to use it even if we tried.
at about 1
she was never a fan
Around 2 years. DS1 wanted to sit in a big seat like his sister.
DD1 was about 2.5
DD2 a little under 1.5. She just never wanted to sit in one..wanted to be just like her sister