If it is a German Lugar then: The information won't come from the serial number. Look at the top of the pistol's barrel as it is pointed away from you. Look at the end closest to you. Do you see a letter, or a four digit number or a two digit number? If you see a 'G' this means it was made in 1935. If it is a 'K' then it was made in 1936.
If you see a four digit number, then that is the year it was made. If you see a two-digit number, then it was made in 1941-1944, see number 41, 42 43 or 44, to identify the year. Hope this helps. 
Checkout web sites, there are experts available on German weapons.
Luger Identification Guide - Rework and non-DWM Lugers (1915-1945) This is one of a series of identification guides for small arms. The 1920 dated and double dated rework Lugers (DWM and Erfurt) are in the 'Lugers - DWM Commercial 1898-1929' Gallery.