That is how age works. Age is not based on years it's based on time. We just used years as a measurement of achievement.
If two people were born a minute apart from each other the person who was born first would still be older. How is this even debatable?
If you were born the same year but different months whoever was born first is still technically older scientifically and legally because one will be the next age before the other. However I’m still kinda neutral, Maybe not at the same time since you both were in the same development era.
Time is relative. I could be older than Christopher Columbus. There is no "older" there is only present and branching time. Babies born 1 milisecond apart are the same age in a relative time and the same age as you and me. Thats just the facts. Feeling uneasy libtard? I would.