Don't.
Parse the strings to DateTime, and compare the year value from there.
Otherwise, you have to cope will all the possible variatiuons on a date format:
19/02/2014
19/02/14
14/02/19
2014/02/19
02/19/14
...
Are all valid versions of the same date in various cultures.
Using Parse allows the system to use the current culture information to start with for a "good guess" as to the actual date format.
If you must play with strings, then look at the String.Substring method to extract just the year - assuming it is always in the same place...
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