Typical age range of early adolescence

What is the typical age range of early adolescence? When does it start and stop? What characteristics typically define adolescents? When you interact with someone, what are the things that make you think, “this person is an adolescent?”
Are the experiences of early adolescents today different from those of adolescents 10-20 years ago? How so?
How do you see yourself engaging in the work of supporting early adolescent development?