Is there a lower age limit to be able to shecht (slaughter animals in a kosher manner)? If so, what is it?
Related question: Is age a disqualification for Shechita? (upper age limit)
The lechatchila age minimum, according to Simlah Chadasha (1:30), is 18 years old, because at that point a person is a "בר דעת" and knows how to be careful with things. This minimum can be bypassed if a person is an exceptional ירא שמים, and is considered to be a גדול (adult; see footnote for technical definition).
What would happen if a minor* slaughtered?
*"Minor" (קטן) for these purposes is defined as younger than 13 years and one day for boys; for women, younger than 12 and a day.
Just to clarify @Shokhet's answer - there is no lower age limit, as long as the child can slaughter and he is being supervised. This is found in Shulchan Aruch 1:5. The Rema there comments that there are those who are machmir not to give a kabala for shchita to someone under 18, just like the Simlah Chadasha says.
The Shulchan Aruch's language is "יודע לאמן ידיו לשחוט" which is more accurately translated as - the child's hands have mastered the skill to shecht, and not the more general - "mastered fine motor skills" as @Shokhet translated.