You can use the strptime and strftime methods to convert them from unix timestamps back into readable dates. Using your example you could use:
| eval timestamp = strptime(Date,"%m/%d/%Y"), Year = strftime(timestamp,"%Y")
The first command takes the Date object and turns it into a 10 digit timestamp of seconds. The second command takes that time and returns the value from that timestamp you want, in this case year. The full list of time variables can be found here:
https://docs.splunk.com/Documentation/Splunk/7.2.0/SearchReference/Commontimeformatvariables
The next step you can use to do stats grouped by Year:
| stats count, avg(Field1), max(Field2) by Year
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