What is the age and value of a rifle made by J Steven Company in Chicopee Falls Mass patent April 1794 serial number 748 hammer lock lever lock?

The "April 1794" refers to April 17, 1894. Stevens didn't exist until the late 1800s. The gun you mention is probably a Stevens Favorite. All Favorites made between 1894 and 1915 carry that "April 17'94" designation. Price depends heavily on condition. The Favorite is quite popular with "boy's rifle" collectors. Ones in poor to fair condition can be found for less than $100. Ones in excellent condition carry prices of as much as $500. Most in average condition sell on-line in the $125 to $225 range. Ones in equal condition are often a bit higher at gun shows.