It depends - on the maximum configured log file size and what Windows is to do when the log fills. By default the initial log file size for all logs is 20MB and when that fills it is overwritten. That being the case your logs from two years ago are likely overwritten and thus gone.
Open the Event Viewer and expand the Windows logs folder so that you see the various logs (Application, Security, System, etc.). Right click on each log type and select 'properties', in there you can change the log file size and indicate what to do when it fills - archiving would seem the best choice for you. You can also see when each log file was created and its current size.