In Korea, there is a strict rule in which those younger must show their respect for those older - regardless of how many years they are older.
In Korea, younger individuals refer to older individuals with titles such as "Oppa," "Unnie," "Hyung," and "Nuna," depending on both party's gender. However, there are times when a child gets admitted into school earlier and becomes friends with children one year older than them.
That is the case for EXO member Suho. Although he was born in May of 1991, he had been sent to school a year early and became friends with kids born in 1990. Because of this, Suho continued to be friends with celebrities born in 1990, such as Girls' Generation's YoonA, fellow EXO member Xiumin, and more.
One fan created an online post explaining the situation with Suho and his celebrity friends born in 1990. The netizen who created the online community post explained, "Suho is born in 1991 but went to school early so he's friends with celebrities born in 1990. The celebrities born in 1991 still treat him as older because of that."
The netizen explained that Minho from SHINee is treated as younger even though he was born in 1991.
Even Seohyun from Girls' Generation is born in 1991 but still refers to Suho as "Oppa."
The netizen who created this post explained they wanted to clarify the relationship between Suho and the idol group members born in 1991 and 1990 because there were a few netizens who were criticizing Suho being born in 1991 but being casual with the idol members born in 1990.
The netizen explained, "If Suho would be friends with those born in 1991 and 1990, their relationship could have been messier. Suho decided to be friends with those born in 1990 because he was in the same school grade as them."
Netizens commented, "So if he's born in May and another idol is born in February, they would still refer to him as someone older because he went to school early?" "I mean, they decided their relationship so, we shouldn't butt in," "I realized a lot of people have a problem with every little thing," "They decided the relationship on their own so whatever," and "I guess haters had nothing else bad to say other than this."