He's been alive since the end of Cell arc, when they wished everyone Cell killed back to life.
That in itself though would be a bit of a retcon.
We know chi is like a force field, and if they want to establish that bullets are only stopped by chi, that's fine, but that's not what's been established previously.
Characters have been shot by surprise before. It's literally one of the first things that ever happened in Dragon Ball, Goku literally says that his body is as strong as steel when it happens.
Indeed. Vegeta has this thing we call "character development" that Goku is completely lacking in. MasakoX made a video about this.