Recommendations

Both main male characters are very wise, and they both respect the main female characters (and how rare it is). If you will watch both of those dramas you will notice they have a similar plot twist, in which I personally think QIHM succeeded more. I think anyone who loved one of those drama will enjoy the other one, though it is up to one's individuality which one he or she will like more.

Both are psychological dramas were there is a family involved. Both have also some mystery involved. Both have a cliffhanger at the end of the drama.

Both have the Genres Manga/Romance/School. Also both of them are pretty cute! However Kinkyori Renai is a relationship between a teacher and student while in Kimi ni Todoke it's between two students.

Both are funny and the stories are about the airline industry. Although Good Luck is mainly regarding a Co-Pilot and Attention Please is regarding a Cabin Attendant.

A Company Man is also an Action/Thriller. In both, the main character is a killer and also they are trying to protect someone.

A Company Man is also an Action/Thriller and it gives a similar vibe to A Man From Nowhere and No Tears For The Dead

Both of the dramas give of the same vibe and both dramas are from OCN.

The guy loves the girl but the girl takes her own sweet time and dates another guy. Both dramas need patience to see OTP together but the wait is worth it!

The plot lines are quite similar however they have their own differences.

The female leads travel to past (Goryeo) in both dramas.
Even though there is so many differences between this dramas.

Both dramas are orientated around the complicated relationships within the family though "What happens to my Family?" veers off to have more in depth relationships for each member in the family they both deal with the same issues with "Yeah,that's how it is" being a more serious drama.

The main girl also cross-dresses as a male during a historical period...

it's kinda similar to this drama but that's only with the whole two different world things I recommend reading some reviews.
The drama is about a girl named Claire Duncan who is absolutely addicted to watching her all time favorite Korean Drama "Taste of Love" and wishes she could live in a world exactly like that, when suddenly she finds herself in the so called "DRAMAWORLD" where she meets another facilitator by the name of Seth Ko who's a waiter in which you think wouldn't hurt a fly but is he really all he seems to be?

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.

Same revenge stuff. If you liked one, you might like the other one too.