Tell me why we should care about milestones, and I’ll give you all the milestones you want. Unless you have a question driving this and a purpose for it, all answers are arbitrary. Is there some way of knowing objectively where people should be at a particular stage of life? If so, that will give you the answer to your question.
Personally, I do not think there is any objective way to determine where people should be. You might be able to do some tests and describe the average development on certain criteria at certain ages, but to move from that to normative statements would be a mistake, I think.
We need flexibility, not milestones. We need roads that work like those in “The Phantom Tollbooth,” not like the Autobahn. We’re humans, not cars. Developmental milestones do more harm than good. They keep people from relating to each other as people.