How to convert different string value to respective 'YYYY' int format?
Get the value from the XML as a string and do some string manipulation in a case statement.

Example with simplified XML:

declare @X xml = '
&lt;YearBuilt&gt;2017&lt;/YearBuilt&gt;
&lt;YearBuilt&gt;New&lt;/YearBuilt&gt;
&lt;YearBuilt&gt;0-5 Yrs&lt;/YearBuilt&gt;
&lt;YearBuilt&gt;70+&lt;/YearBuilt&gt;
';

select case
         when T.Value = 'New' then year(getdate())
         when T.Value like '%Yrs' then year(getdate()) - cast(replace(stuff(T.Value, 1, charindex('-', T.Value), ''), 'Yrs', '') as int)
         when T.Value like '%+' then cast(left(T.Value, charindex('+', T.Value) - 1) as int)
         else cast(T.Value as int)
       end
from @X.nodes('/YearBuilt') as Y(X)
  cross apply (
              select Y.X.value('text()[1]', 'varchar(10)')
              ) as T(Value);