I cannot brain. So Voids are actually scattered pieces of Mana that infected other people's heart. So why it only infects people under 17 years old? Mana was such a pedo at that time?

I know they tried to follow Evangelion's "All pilots are kids 14 years old" but that was due to them being born after the 2nd impact

In a post with a picture saying "Anime in Progress," Nitroplus has announced following the end of today's final episode of Guilty Crown that the limited edition of the PC game Guilty Crown Lost Xmas will also include a DVD with an animated short. The anime will run about 12 minutes and be animated by Production I.G. It will not be about the game, but instead will be based on a special script written by Nitroplus exclusively for the short.

It was also announced that the game's cast has added Ayahi Takagaki as Past to the list of Takahiro Sakurai as Scrooge, Kana Asumi as Carol, and Yuu Kobayashi as Present.

The limited edition will be released alongside the regular edition and will also include a box, a digi-case, a special DVD which includes the anime short, a special booklet of rough sketches, and a two sided "another jacket sheet" for 7140 yen.

the OVA is a part of the Lost Christmas VN story, inception 

if you can read katakana and hiragana, then you can try the VN.
it's quite simple and the conversations are very anime-like, so you should be able to understand it
(not to mention the length is very short, probably can be finish within 2 hours )