The Remington Model 12-C, which features an octagon barrel, was produced from 1909 to 1936. To determine its age, you would need to know the specific year it was manufactured. For instance, if it were made in 1920, it would be 103 years old as of 2023.
That's a Model 12C made in 1913, in mint condition it's a solid $1,200 but value drops QUICKLY in lesser condition.
It was made in 1929, you didn't mention what caliber probably 22 rf so with a octagon barrel it's a 12C (if it is a .22 WRF / REM SPl) then a 12CS. The value is greatly dependent on condition in mint condition as high as 1,200 drops to 1/2 that price at 90% and then drops quickly from then on.
1927, check related links for date code on barrel look-up month/year.
1929, it's date code stamped on the barrel see related links if you want to know the month as well.
1925, check the date code stamped on the barrel. Remington Society of America, Manufactured Date link has the details.
1920
1914
1911
Probably 1925 but check the data code stamped on the barrel. Check the Remington Society of America web site manufactured date link.
Early 1920.
Manufactured: 1913 The manufacture month and year of a Remington rifle can be determined from a letter and number code stamped near the back of the barrel on the right side. If your Model 12 is not marked 12A, 12B, 12C, 12CS, 12D, 12E, or 12F, it is a basic Model 12.
Late 1911