Late 70's. Your best bet is to call Colt.
Service Model Ace
Service Model
if it's a New Service model it was made about 1920
1978
The serial number YC00F09066M indicates that the bike is a GT model, likely manufactured in the year 2000, as suggested by the "00" in the serial number. The subsequent numbers and letters typically represent specific details such as the production batch and model variant. To determine the exact model and specifications, you can consult GT's customer service or reference their database with the serial number.
To perform a GT Dyno serial number lookup, you can contact GT Bicycles customer service with the serial number. They can help you identify the model and year of your bike.
Without a serial number there is no way we can tell you. Get the serial number, contact Customer Service at Winchester.
Check Ruger website, under customer service, historical data. They have production dates by model, by serial number.
To determine the model of your Cannondale bicycle, look for a serial number on the frame. You can then contact Cannondale customer service with this number to identify the specific model of your bike.
Browning.com has a sn function under customer service.
That serial number in not in published data for the Service Model. Recommend you call Colt.
model number is always smaller than serial