Board Thread:Legitimate Canon Questions/@comment-71.224.147.115-20150406011412/@comment-4091815-20150406033326

We don't have birthdays for Scott or Stiles.

Lydia's birthday is in March as seen in Party Guessed. Her mother says in Time of Death that Lydia is due to turn 18 in "only a few weeks" making her 17 at the time of the of the Season 4 episode.

Victoria Argent says Scott is "a 16 year old boy" in Frenemy during Season 2 meaning (if she is accurate) that he was 16 in March of 2011. Depending on his birthday (not given in official canon) he could still be 16 or have turned 17 in Season 4.

I can't find a direct reference to Stiles' birthday at this moment. It is assumed he is the same age as Scott.