When should I ask?

My SO and I went to a wedding yesterday and it got us thinking about our wedding. We aren’t yet engaged but we talk about wedding stuff sometimes. He told me who his best man is going to be and I told him who I thought would be perfect as a maid of honor and brides maids. He told me to start asking but I think it’s too soon since we aren’t yet engaged. Would it be appropriate to start asking the ladies that I want in my wedding if they would be my brides maids/maid of honor?

Thanks everyone for the advice. I agree with you all and I thought it was weird to even ask when we weren’t engaged yet and I explained that to my SO but I don’t think he understands how strange it is to ask someone to commit to something we haven’t yet begun to commit to. I will definitely keep those ladies as a thought for when the time comes but for now, I’ll leave it at that, just a thought.