The ages (and dates of birth) of each of the Sidemen on this wiki have been sourced from various websites and videos. However one member in particular, Simon (also known as miniminter) has an age which fluctuates between 21 and 22 depending on the website. We know for a fact that his birthday is 7 September, but the exact year is unknown. Some say it is 1992 (which obviously makes him 22) whilst some say he was born in 1993 (thus making him 21).
According to these two sources, Simon is 21:
However according to this video (around the 7:47 mark), Simon says that 1992 is "[my] year" making him 22.
Since Simon said this himself, this is the age that we are going with; but if you find anything else that disproves this, please don't hesitate to leave me a message on my talk page!