IC Information;Character Name; Himari Takakura
Canon; Everyone Loves Momoka: the Anime Mawaru Penguindrum (
wikipedia;
tvtropes)
Canon Point; Post-series, after having found Kanba and Shoma's note inside her stuffed animal.
Age; While not implicitly stated in the anime (although I have yet to check the novel translations, but some quick English + Japanese Google-fu brought up nothing as well), it is generally agreed by fandom that Himari is 13-years-old. There are also various hints and signs in the series that point to her being at
least around this age. First off, she is stated to be younger than her brothers, who are both 16-years-old. Secondly, the last time she saw Hibari and Hikari she looked pretty young (as in, elementary school young), and it was later stated that she stumbled upon them as Double H two years later, by which point she already looked about the same age she is in the main series. Then, at the end of the last episode, she's wearing a uniform that doesn't correspond to either of the high schools shown in series, so it might be safe to assume it was a middle school uniform she was wearing.
( Your onii-chans were here. Kanba is a loser. )