Javanino, there are date codes on many German, Belgian, and Italian guns. Proofmarks on British guns provide at least a range of dates. French guns are much more difficult in that regard. After you've seen a bunch, you can make a very rough estimate: before WWI, between the wars, or post-WWII. But unless the maker is still in business and has records--and there are a lot of "no name" French guns, and some current makers lost their old records in the war--you're pretty much out of luck.