How do i find out how old my toy dirt bike is?

I have a die cast yamaha toy dirt bike my grandmother gave to me, It's still in the package, and i want to know what year its from and how much it is worth.. any ideas?|||Antiques Road Show .com/toys to value it.To find the year look for a copy right date on the package or depending on the manufacturer it will be cast in the bottom of the toy.