Monica Rambeau AKA Spectrum joined a police academy at the age of 18 and was exposed to extra-dimensional energy at the age of 20 and at that age joined the Avengers. She is 4 years older than Miles.
Not much is known about Monica besides the fact that she was born and raised in New Orleans, Louisiana. Her mother, Maria Rambeau, was a excellent seamstress, while her father, Frank Rambeau, was a great fireman.
Monica was a police officer and a ship captain in the New Orleans Harbor Patrol. One fateful day, she found a criminal scientist creating an energy disrupting gun. She tried to stop the scientists and absorbed the extra-dimensional energy and became a superhero.
Joining The Avengers
When learning about her powers, she met Spider-Man (Peter Parker) who introduced her to the Avengers. When she had enough training, she not only became a full time member, but soon became one of the leaders.
Meeting Miles Morales
While on a mission to track down the criminals who gave her the powers she has now, she met up with Spider-Man (Miles Morales), who was destined to take them down. They got into a quarrel and a short dispute that turned into a short fight. They were both attacked by Juggernaut only for both of them to be saved by Thor. She gave a quick glare at Thor and when they got to Avengers Tower, she said that she had it under control. When destiny arrived for Miles, Monica said he was too young, but was reminded that she was young when she started as well.