There are some discrepancies about Si's birthday, which he celebrates his birthday within the series' on at least two occasions. In episode nine of Meteor Garden, his birthday is stated to be on the 31st. Furthermore, taking into account episode eight, the month is likely May, which would make his birthday May 31. In episode two of Meteor Garden II, his birth date is shown to be June 16, 1980 on his ID. However, this is considered non-canon.
It is revealed in episode fifteen that Si's and Shan Cai's initial two month dating period is almost up. This indicates that two months have passed between episode twelve and fifteen, which also makes the month likely August.
Si likely turns twenty-one in episode ten of Meteor Garden, partly based on the F4 being three years younger than Jing. The rest of F4 are most likely twenty-one as well.
Shan Cai is assumed to be around two years younger than the F4.
The ages of Shan Cai, the F4, and Ye Sha are listed on the official Meteor Garden II website.[1] This information, however, is erroneous and not considered canon since it does not align with the information from the series'.
Ye Sha's age can be considered canon since it is not contradicted with other information.
↑Shan Cai is around 19 years old in 2001 and her parents married 20 years prior to the beginning of the series, making 1982 likely the year she was born.