Continuity mistake: All of the rangers were bestowed their powers when they were young children, including Emily's older sister. If the rangers were all selected when they were the same age, Emily should have been considerably younger than the rest of the team.
Suggested correction: I don't believe it was ever explained when the team was given their powers, so we can't know for sure that Emily would be the youngest. We learn during the season that the team was pre-selected and trained to become Rangers, but not when that took place.