Both shows are fluffy and light with a lot of heart! Watch for the adorable OTP chemistry and coming of age story between the leads. Also, I don't remember ever hating the 2nd leads as the episodes progressed on both shows.
If you enjoyed the slice of life feel that Age of Youth offered then Dear My Friends is a perfect follow up for it. I would say the obvious difference would be their age, otherwise both dramas have a strong emphasis on friendship and sisterhood, coming of age for the younger set and coming to terms with their age for the older women. Their stories and their feelings are so relatable.