My boy has refused to go in a highchair for a long time. He is however still in his cot and uses the pushchair regularly (he'll start walking but often ask to go in so I take it just in case). You do you! When he reaches the limit have you considered one of the booster seats that strap to a dining chair?
I do for messier meals. Lunch and some breakfast she will sit at her little table. Otherwise she is up wondering round etc
We had a booster seat with straps that attached to the chair but now we have a toddler chair at the table. He doesn't make much mess anymore.
Im not the type to baby him as I want him to develop at every chance possible. He has a bed (not cot). But still use the pushchair along busy roads because of the way he is