This is very much similar to Familiar Wife.
- Both are tearjerkers (I cried in both)
- Both are great second chance romance dramas
- Both are centered around male characters sort of traveling back in time because they are tired of their current situations with their wives . For 18 Again, ML travelled back in time into his teenage body, while in Familiar Wife the ML travelled back in time to chance a crucial choice that changed the present.
- (My favorite) Both MLs got to see all the small details they missed when they were together with their wives. Both MLs get to realize their mistakes, regretted their decisions and actions, and learnt that they still love their wives more than anything in the world.

If you really love second chance romance dramas + going back in the past elements, then these 2 dramas are good for you.