If you send an inquiry to Kubota customer service through the Kubota website, they will usually respond with the date of manufacture, the date of sale, and the original selling dealer. A Kubota dealer can do the same thing.
A "get it close" method is to compare the serial number to that of tractors with published serial numbers and dates. The serial number are sequential. Some used tractors for sale site list serial numbers and dates.
If you get the engine serial number, I believe that you can pin down the engines date of manufacture.
As an example, I own a 2017 B2650. It was made in 2016, and first sold in August of 2017. In tractor land, that makes it a 2017.