Board Thread:WARNING ALL USERS False Info\Spoilers/@comment-74.73.18.44-20130723204915/@comment-13965604-20150802020906

AlphaOfAlphas wrote: Speaking of age, how come young Derek didn't notice that Kate aged?

Good question. It was never addressed in canon, that I recall. I can only assume he was just so relieved to find someone familiar that he didn't notice and/or willfully ignored it.