Yes, the first digit in the serial number indicates the year. Based on a single set of bottle bosses, no pump peg, a clamp front derialleur and the all chrome fork, I'd guess it is closer to the mid-1980s.

Edit: Agree with Cyclotoine, no month or size in the serrial number. The remaining digits indicate the frame number for the year. At the time, Marinoni was only building about 1200 frames a year, so a five digit serial number would be correct.