Ni Shi Wo Zui Tian Mi De Xin Shi (2021)

A 27 years old postgraduate student majoring in Psychology, Tang Wei Wei, could not pursue her dreams due to family's opposition. Her father intended for her to be married before she turns 28 years old and suspended her academic dreams. Lin Ran, 6 years younger brother, volunteered to help her. They later turned into couple. Here the sweet journey start
so this drama has every elements that suits for the other.

Both leads are long time friends, with the FL older than the ML and always treating him like a younger brother while he has a long hidden crush on her. The two end up living together and the FL starts to reciprocate.

It's like Irreplaceable love cuz they are like brother and sister ,the girl is older than the guy and the guy had some kind of allergy .
The allergy in" irreplaceable love" is of egg while in " my sweetest secret " is of sweets .
Yes they have similarities.

FL and ML have an age gap in both dramas, with the younger ML falling first, but the FL viewing him as a younger brother for years before finally accepting him.