This is the 1978th most frequent Russian word.
старший
Elder; senior; older.
In this sentence, 'старший' ('elder') is used as an adjective to indicate that the brother is older than the speaker.
Мой старший брат учится в университете.
My elder brother studies at the university.
Here, 'старший' ('senior') is used as an adjective describing a higher rank or position in a professional role.
Она работает старшим инженером в крупной компании.
She works as a senior engineer at a large company.
In this instance, 'старший' ('senior') modifies 'staff' to specify individuals with more experience or higher ranks.