How old is Dupli-Kate?

I had finished the season recently (it's great!), went to google some things about the comic's main characters out of curiosity, so I found out the Immortal eventually marries Dupli-Kate apparently, so.... uh, how old is she actually at that point? Because the "Teen Team" implies that at the beginning of the comic / the show they all are teenagers, and it would be kinda creepy for a 3000-year-old guy to marry some 18-year-old kid.

Sorry for a silly question, I tried to google it by myself, but nothing about her approximate age showed up, so I wanted to get a more or less straight answer.