I am big. I am 10 years old!
They are Egyptian. They are from Egypt.
I am big. = I'm big.
You are my friend. = You're my friend.
My mum is a doctor. = My mum's a doctor.
We are doctors. = We're doctors.
They are Egyptian. = They’re Egyptian.
For negatives add ‘not’. The negative of 'I am' is 'I'm not' or 'I am not'.
I’m not 9 years old!
I am not 9 years old!
They’re not English.
They aren't English.
They are not English.
She is not a teacher.
She’s not a teacher.
She isn't a teacher.
We say... We don’t say...
I'm not 9 years old. (NOT I amn't 9 years old.)
Are you 9 years old? (NOT You are 9 years old?)
Are they English? (NOT They are English?)
Is she a teacher? (NOT She is a teacher?)
(If you want to show surprise you can say Pronoun + be +? as a question, e.g. You're 9?)