Ah, yes...welcome to toddlerhood!
Something they like one day is completely wrong the next. Fun, huh?
I don't think it's ever too young to introduce the idea of table manners. The trick is that they need to be age-appropriate. It's not okay for a 6 yo to eat yogurt with his fingers, but it's fine for a 15 mo, KWIM?
Around here, meals are always at the table for both kids. I don't eat anywhere else so neither should they. If you feel the same way, you might consider only offering meals at the table and not in the lounge anymore. High chair, booster, chair with a cushion...doesn't matter, as long as it's at the table.
My DD is 16 mo and has days where she swats me away if I try to feed her with the spoon. That's when I undress her to the diaper and let her do it all herself. She makes a mess and I have no idea if she actually gets any in her mouth, but she's learning and that's okay. Even if the dessert spoon is big and awkward, so be it. She'll figure it out. I'll hold a baby spoon and a dessert spoon in front of her and she'll grab what she wants...even at this young age, they're capable of making choices and like to think they're in charge. I give her choices at mealtimes when I can, too. I'll hold a banana and a grape in front of her. She'll grab which one she wants, so that's what she eats. Obviously, I control the choices she's offered, but she really likes having some element of control.
Does that make any sense?