if a person discloses selling weed to minors to the police, which happened 4 years ago, can he be arrested?

You raise two issues. The Prosecutot can charge you with the distribution after four years. However, from a practical viewpoint, this will not occur unless there are special circumstances. The bigger issue is the impact upon your police application. We have advised candidates to be candid. However, your situation may be disqualifying. Please call to discuss. Ed Dimon