Update single_session.rst

docs/tutorials/single_session.rst

@@ -112,7 +112,7 @@ The Session Start Time in the **General Metadata** section is already specified
   :alt: Metadata page with invalid Subject information
 
 
-However, we still need to add the Subject information—as noted by the red accents around that item. Let’s say that our subject is a male mouse with an age of P25W.
+However, we still need to add the Subject information—as noted by the red accents around that item. Let’s say that our subject is a male mouse with an age of P25W, which represents 25 weeks old.
 
 .. figure:: ../assets/tutorials/single/metadata-subject-complete.png
   :align: center