How do you feel about turning 40?

Soon i will be turning 40 and i feel blessed I made it this far Dont get me wrong but a part of me feels sad. I can’t help it Im sorry. I feel my life will soon be over. I don’t feel 40 but i work with young girls in her 20s and I can’t help to feel im old. I don’t know why. I know i am being ridiculous but it just a feeling that comes over me and takes over. Im very grateful that i made it to this age because not everyone gets that chance but im also afraid. Its a new chapter in my life. Can anyone relate to what im feeling? How do you cope with that feeling? Thank you.