User blog comment:Paul.rea/Teen Wolf News 081314/@comment-199.168.73.11-20150620221930

The current timeline bases that the first three season were in 2014 (second semester of sophmore year and then through the first semester of Junior year), then season 4 is set in the begining of 2015 (second semester junior year), and season five at least starts in mid 2015 (begining of senior year).

So, season four papers say that she was born in 98; 1998+9=2007+8=2015. She should still only be 16 in s4 and turning 17 in s5. This would put her a year behind everyone else in school as well, shich they /obviously/ can't have.

Then again, Natalie Martin said that they were only a few weeks from Lydia's 18th birthday and that makes zero sense, so who even knows anymore.