title: Issue with converting a pandas column from int64 to datetime64
body: <p>I'm trying to convert a column of Year values from int64 to datetime64 in pandas. The column currently looks like</p>
  <pre><code>         Year
  
           2003
           2003
           2003
           2003
           2003
           ... 
           2021
           2021
           2021
           2021
           2021
  </code></pre>
  <p>However the data type listed when I use <code>dataset['Year'].dtypes</code> is <code>int64</code>.</p>
  <p>That's after I used <code>pd.to_datetime(dataset.Year, format='%Y')</code> to convert the column from int64 to datetime64. How do I get around this?</p>