Our DS1 got shifted out of his highchair and into a booster seat when he was 19mo, in order to make room for DS2 (who was 6mo at the time).
Consequently I was a bit surprised to see a photo of one of DS1's friends (who is 2 weeks younger than him) at his family dinner table in one of those giant highchairs which you'd happily put a 6mo baby in (i.e. very supportive and all-encompassing). I think his mum may have been spoonfeeding him too - if I tried that with DS1 he'd grab it off me with a 'Mother, what are you DOING?' look 
The little boy is physically capable of feeding himself (I've seen him do it) and NT as far as I'm aware.
I do understand putting toddlers in highchairs when you're out to imprison them - I do that myself. But at home? At this age? Is that usual? I'm not sure whether we just moved DS1 up really early or what.
I'm not looking for a row or to be told how unpleasant I am; I'm just curious as to other people's outlooks. Thanks in advance!