You, or the agency handling your analytics, should recently have received an email from Google Analytics about an update to their Data Retention policy. Specifically, and effective from May 25th, the default data retention period is for 26 months. But it can be changed to anything from 14 months to well, never. The default retention period is 26 months.
To change your Data Retention settings, go into Admin –> Tracking Info for the Property in question.
Before you panic, note that the data retention period is for user and event data (such as cookies), not broader ‘aggregated’ data. But still, if you’re a data squirrel like myself, you’ll want to hang on to that juicy data for as long as possible. Except that strictly speaking, with Google Analytics Standard, your data is only guaranteed to be retained for a mere 25 months anyway!