Information
Manga sidestory "The Beginning Man." This is as-of-yet impossible to get a hold of in its entirety at all, much less fully translated; only a few sneak previews of it have surfaced, and those have been translated. Relevant to this application:
"After my family fell apart, I was a sniper until I came to CB."
The furigana indicates "sniper"; the kanji for the same means "assassination work." This has been interpreted alternately as "he's talking about the sports shooting 00P mentions he competed in" or "he used his skills with the rifle as an assassin." For this application, I've gone with the latter, expanded on just enough to make sure it fits his character. I think it would explain a lot about how he went from an adorable and innocent kid to someone with no compunctions about fighting and killing to change the world. Also, the other interpretation would have him being the only Meister who was neither created (Allelujah, Tieria) nor trained (Setsuna) for combat prior to his recruitment into Celestial Being. He doesn't really come across that way in the show.
Edit on more translation: That particular line is Lyle speaking, and it reads, "I read my brother's data. After our family became asunder, he became a [furigana: sniper / kanji: assassination work] until he joined CB. It seems my older brother thought that the dirty work was only for him."
The combination of that kanji plus the proximity of Lyle's comment about "dirty/unpleasant work" makes it clear that he's not talking about sports shooting competitions. However, the other details we've learned about Neil's background and character indicate that him being a full-time amoral assassin isn't feasible either. We're unlikely to know the details until further background is released. For now, I stand by the personalized version I used in the application.
Summary of 00P Chapter 13, by
sapphire_hime:
Grave (he's the intelligence head/person for CB) needs to decide on the first Meister candidate. His data is already in data, stating the tragedy of losing his family, and having one family member left. He seems likely to be influenced because he hates terrorism. He also has an excellent record in sports shooting and has competed.
Grave spends 3 hours tailing Neil. He thinks he's grown up decently. He has a feeling Neil would be the sort to value his teammates. Which is essential, since there meisters need to share a solidarity between them (riiiight). And he could tell he's the leader sort. There was so much Grave understood better than the cold computer data that stored Neil's information.
Ian, Moreno, and Hixar are asked about what they thought of Neil as a candidate. Out of the team, Chall was the only one who didn't want to meet the new Meister. She couldn't bear to meet him after losing her old companions. Grave thought that when Neil becomes a meister, Chall's heart will heal. That's when he decided on recruiting Neil. (He also swears Ian and Moreno to secrecy.)
Neil is then recruited instantly, at age 19.
Links
The third novel On "The Beginning Man"Gundam 00 on the Gundam Wiki