70s and 80s, your engine looks to be original so look at the ID tag and the 1st number on the last set of the serial number is the last number of the year model. Yours looks like a 70s engine from the decal, say the number is 2 and that would make it a 72 model. Peekster a member here is the expert on these and could nail it down easily, I'm just a guy who likes them and all minibikes of which I have way way too many.