If you have tried cocaine once when you were 18 and am now 22 almost 23 would this be an automatc disqualification for getting on the police force?

No. Chronic use of narcotics would because they could still be detected in your blood stream, and found in a routine screening by the hiring agency. It would be very unlikely that they could even detect it if it was a one time thing from a few years ago. It wouldn't even be worth mentioning during an interview.

That would depend on the policy of the department you are trying to get on with. I've been in law enforcement for nearly 10 years. Most of the agencies in my area will allow applicants who have experimented recreationally with marijuana, and possibly ecstacy (MDMA). However, any experimentation with cocaine, heroine, LSD, mushrooms, or methamphetamine has been know to disqualify individuals from becoming law enforcement officers in my area. I have known people who were disqualified for becoming a police dispatcher because they have used ecstacy (MDMA). For those out there who think, well how well they know? At least in my area, polygraph and/or voice stress analysis is used as a requirement for hire, and prior drug use is asked about.