China's social media platform WeChat was abuzz on Saturday and Sunday with people posting photographs of themselves aged 18.

The trend showed many Chinese readying themselves for 2018 in nostalgic mood.

But why 18?

Because, it is said, the youngest members of China’s 90s generation, those born on Dec.31, 1999, officially attain adulthood on New Year's Eve.

For some, this milestone suggests a generational shift.

"Now the stage has been set for the post-00s generation," said an Internet user.

For many, posting the old photos was not just a coming-of-age party, but an occasion to lament the passing of time. "I was young and chubby. Now I am old and thin. I would rather exchange the lost weight for the lost time," said one wistful WeChat user.