I think that it all depends on the age and gender. I think.
You introduce the younger to the older; the male to the female first.
The younger person is always introduced to the older person. Mrs Smith, may I introduce (my niece) Mary Jones. Mary this is Mrs. Smith. Use the name the younger person should call the older as a courtesy to them. You may add relationships as I have in brackets if they are relevant.
The opposite of older is younger.
He had older and younger siblings.
I don' know if he was older or younger
younger : plus jeune older : plus vieux
yes he has a younger sister and an older brother yes he has a younger sister and an older brother yes he has a younger sister and an older brother
the has and older brother and a younger brother > Jelani ( Older Brother) Makiah (Younger Brother) Maya (older Sister)
= Older father, younger mother =
older gilberte younger Jacqueline
Albert Einstein was the younger sibling to an older sister.
younger