Yes, freckles start developing in your teens and do get darker.
Using sunscreen is essential to prevent them from darkening, increasing in numbers and recurring. Sunscreen has to be applied every 2 – 4 hourly.
Pigment lasers are used to remove these freckles, however they might require 1 – 3 sessions of laser treatments. Of course, diligent sunscreen application after laser treatments helps to prevent recurrence. Thanks.