With my 3 kids they were in a walker at around 4 months old,as long as they are at and age they can support their head well its fine
I would say as long as they can support their head. We never used a walker with my daughter since we couldn't make it short enough for her legs to eger touch and she was walking on her own before she could touch. We only used one of those jumper bouncy things.
My brother got in one about 4 months old. He could support his head. He walked very early and loved his walker.
I was told by an austism coordinator walkers are bad but I disagree.