Recommendations

The cast start as dating couples in CD and friend couples in L&J.
They go on dates with the others, change their dates too.
In CD, couples try to find if they r still in love with their partners or they want to start a new relationship with the other. CD is a show of couples, hence it's realistic and portray real-life problems between them, Whereas in L&J, they try to find love between friends or other partners. This is more of crush and lust, in my opinion.

In both dramas the male leads loose their memories, personalities change, and are taken in by the FLs.

Both dramas center around a group of housemates who are friends. If you like that supportive environment in friend groups, then you might have fun with both dramas. Each also explore subplots of dating scenarios and housemate struggles. Even the homes they live in are kind of similar from the outside.

Differences: In Age of Youth, they don't all start out as friends. While Age of Youth has its fun and fluffy moments, it's also a drama with a serious side, unlike Crash.

Similar ??. Set in the time where China was under Japanese occupation the storyline speaks of how the two snipers become embroiled in the fight against each other first then against the Japanese.

Deep love between main leaders
Virtuous and suportive Empress
Power struggles
Diffilculties of poligamy
Side couples
Harem fights

Young ML/older FL
Boyhood crush
FL is an independent career professional
ML returns from abroad
Fated Boy is a less melodramatic version and the chemistry between the leads is playful and electric. Also family and friends are very supportive

Both these dramas focusbon a strong female lead who is the CEO of a corporation.

Also, another similarity that can be noted is that in the two dramas, the leads enter a marriage of convenience which eventually leads to their falling in love.

Fl is older in both (Stronger in Thai one)
ML chases the female lead first
Childhood crushes
Superb playful chemistry between the leads
No annoying/evil/screaming characters rather good supporting cast in both
Both same duration ~32 hrs

Both are second chance romance stories where a divorced couple learns to see each other in a new light and begins to heal old wounds.

Both are romances in which the ML has feelings for the FL from the start but initially hides them due to his childhood trauma/inability to open up to people. Both MLs seem quite cold and distant but once they open up to the FL they are adorable to watch

Both ~10 years age gap and as per title the older FLs are quite rational
Strong hardworking FLs
The leads are great actors
Both First love (for ML :P)
Pestering moms in both (More so in Chugakusei Nikki)
Chinese one is definitely a lighter watch after Chugakusei Nikki

Both have Strong FLs driving madly towards their aim and a cute side couple
Both are office romance , Thai one is in Law firm and spends more time on the leads than Search WWW
Both are have a similar practical take on age gap relationships

Both movies are quirky and sarcastic, and they feature weirdo MLs that work in a place that looks innocent on a surface (laundry, bathhouse) but is, in fact, involved in crime.

- just the vibe of these dramas are slice of life/comedy/some seriousness
- great chemistry between the friend group
- although the plots are completely different, they both hold warmth

-Similar Revenge Plot. ML comeback etc.
-Rivalry
-Flashback Romance
-Period Dramas
-Strong Male Lead
-No peace in their town(Kom Faek) while the King is worst in Joseon(Queen for Seven Days)