1967 was the first year for the color Campus Green. These small juvenile bikes didn't have serial numbers that could be dated. Only way is to pull the crank to get a close idea of year from the crank casting date along with comparing certain features and color of the bike to the catalog images.
1968 Casting. Campus Green was not offered on the Pixie in 1968 so yours is most likely a 1969 model. There may also be a date on the fork's left leg, inside just above the axle slot. Month and year. ( 2-9 )