okay, i've seen a couple of comments about the confusion of the ages of (name) and some of the other characters. hopefully this will help you figure it out.
(late) s2: 8
s3: 9
s4-s8: 10
s9 (ep1-ep5): 12
s9 (ep5-ep.16): 18
s10-s11: 19
hope this makes sense and helps you understand the timeline. thanks for reading!