If you can has the "Keglined" logo on it and if it's from that period, you might be able to read the date code. The earliest pull tab (an Iron City) was sold in 1962. Then it dates from the mid 1970s until the early 1980s. Does it have opening instructions on the side of the can showing how to use a church key?Schlitz started using them in 1963 and other brewers quickly followed. Most brewers got rid of these by 1942, but a few continued to use them after the war.
Look along the seam for the year on most Schlitz cans.
Look and see if there is a tax statement on the can, along the lines of "Internal Revenue Tax Paid" or "Withdrawn Free of Internal Revenue Tax" if so, then the can dates before March 1950.
The exceptions are fake beer cans made for collectors during the 1970s.
General Pulaski and Milwaukee Premium are the most common of these FAKES. If it has the actual patent numbers listed, then it dates post 1945.
There are four types of cone tops: Low Profile, J-Spouts, Crowntainers, and High Profile cans. Check the wonderful Crowntainer Central page for detailed info on dating crowntainers by such details as paint types. One company, American Can, made high profile cones with flat bottoms in the 1940s.