diff --git a/CHANGELOG.md b/CHANGELOG.md
index 865ecff09..588a59ab8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,7 +4,8 @@
 
 ### Fixed
 - Fixed invalid CSS properties in documentation assistant toggle that prevented proper positioning on displays ≥1400px wide. @rly [#2151](https://github.com/NeurodataWithoutBorders/pynwb/pull/2151)
-- 
+- Expanded documentation for the 'age' parameter to include age range examples and clarify usage. @rly [#2161](https://github.com/NeurodataWithoutBorders/pynwb/pull/2161)
+
 
 ## PyNWB 3.1.3 (December 9, 2025)
 
diff --git a/src/pynwb/file.py b/src/pynwb/file.py
index c2fd317ca..d3c044785 100644
--- a/src/pynwb/file.py
+++ b/src/pynwb/file.py
@@ -78,8 +78,14 @@ class Subject(NWBContainer):
         {
             "name": "age",
             "type": (str, timedelta),
-            "doc": 'The age of the subject. The ISO 8601 Duration format is recommended, e.g., "P90D" for 90 days old.'
-                   'A timedelta will automatically be converted to The ISO 8601 Duration format.',
+            "doc": (
+              'The age of the subject. The ISO 8601 Duration format is recommended, e.g., "P90D" for 90 days old.'
+              'A timedelta will automatically be converted to The ISO 8601 Duration format. '
+              'If the precise age is unknown, an age range can be given by "[lower bound]/[upper bound]" e.g. '
+              '"P10D/P20D" would mean that the age is in between 10 and 20 days. If only the lower bound is known, '
+              'then including only the slash after that lower bound can be used to indicate a missing bound. '
+              'For instance, "P90Y/" would indicate that the age is 90 years or older.'
+            ),
             "default": None,
         },
         {
@@ -1152,4 +1158,4 @@ def ElectrodeTable(name='electrodes',
                    description='metadata about extracellular electrodes'):
     warn("The ElectrodeTable convenience function is deprecated. Please create a new instance of "
          "the ElectrodesTable class instead.", DeprecationWarning)
-    return ElectrodesTable()
\ No newline at end of file
+    return ElectrodesTable()