Give it at least five years since any use, then start applying. It will come up in backgrounds and polygraph. DO NOT LIE, that will DQ you forever. Most agencies have some flexibility with mj.
While waiting, do things that will show maturity and solid decision making abilities. Volunteer with the local Red Cross (good training anyway) or animal shelter.
Consider time in the military, either active or reserve. The veterans points will help you get hired and the military will give you a chance to show maturity. There are other benefits to serving also. Many cops are still in the reserves.
Best of luck
If You Heard The Shot, You Weren't The Target