It is an old Russell Barlow. There are imitations out there but your is an origianl. I can't really tell how old it is but if it was in better condition it would be worth a lot of money because they were made in the late 1700's into the 1800's. The following came from a barlow website.
"John Russell may have been the first American to manufacture Barlow knives. The John Russell Company, now the Russell Harrington Cutlery Company of Southbridge, Massachusetts, first made Barlow knives at their Greenfield Massachusetts, factory in 1785. They were called the Russell Barlow knife and instead of the word BARLOW on the bolster, they were stamped with Russell's mark, an R with an arrow through it. Today these Russell Barlows are valuable antiques."