Question: Age Relate Legal Issues

i had a legal question and thought of yall. can you clarify some age-related legal stuff for me? here are my questions.

1. i know that up until a certain age (16), arrests do not go onto your record. is that age 16 as in, if you're 16 or older, it goes on your record, or if you're 16 and under, it does not go on your record?

2. in terms of forming affinity groups / being arrested--at what age are you put into an "adult cell" when you're arrested and held, and at what age are you held as a juvenile? i'm thinking of this in terms of a "buddy system"--it seems like people should not be "buddies" with someone who will be going to a different place than them in the case of an arrest.