According to what I found, although they are still around today, they date back to the late cretaceous. In other words, to the time just before the dinosaurs became extinct. About 10 million years before their extinction.
The shell in your photos looks pretty old, like it could be in the millions of years, particularly with those tiny impressions of other creatures embedded in the surrounding rocky material.
If you’re really interested and want to find out its approximate age, try this site below. Someone there might be able to ID it for you.
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“If you have a shell or a shell fossil at home and you just can’t place an identification label to it, or is your snail doing something and you’re not to sure just what, here’s where you might get some help. I am but an amateur collector myself, but there are many good conchologists and malacologists that may be willing to help you.
Send your photos and collection data, if you have any, to me, Avril Bourquin. I will set up a file page for your shell or fossil shell then people can contact you personally in regards to their idea as to your shells proper identification. Please try to keep your jpg files small.
This kind of service is also available from some other GREAT shell collectors and dealers on their web sites. You may wish to seek out their assistance as well. Contact information for some of these sites and people is located at the very bottom of this page.
Good luck in getting that definitive identification on your treasured shell or shell fossil.”
http://www.manandmollusc.net/id_help.html