A "stereotype" is a common idea about a group of people. For example, people have stereotypes about different nationalities:

• Americans are loud.
• Russians drink a lot of Vodka

...and so on.

People also have stereotypes about certain professions (like police officers and lawyers), different regions (Northereners, Southerners, etc.), races, age groups, and so on. 

When a person follows the stereotypes about a group that they belong to, you can say that they are "stereotypical":

He's a stereotypical teenager: moody, immature, self-absorbed.

You can also use the phraes "your stereotypical ___":

A: What's she like?

B: She's your stereotypical fitness instructor.

This means "she fits the common stereotypes about fitness instructors".

Stereotypes are usually negative, and it's usually not a good thing to admit that you have stereotypes about a group of people.