diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1acffb8..74d7323 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## 4.0.0 - [Unreleased]
+
+### Changed
+- X10D: `DateTime.Age(DateTime)` and `DateTimeOffset.Age(DateTimeOffset)` parameter renamed from `asOf` to `referenceDate`.
+
 ## [3.2.0] - 2023-04-03
 
 ### Added
diff --git a/X10D/src/Time/DateTimeExtensions.cs b/X10D/src/Time/DateTimeExtensions.cs
index 2993b03..a89e613 100644
--- a/X10D/src/Time/DateTimeExtensions.cs
+++ b/X10D/src/Time/DateTimeExtensions.cs
@@ -30,9 +30,9 @@ public static class DateTimeExtensions
 #else
     [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
 #endif
-    public static int Age(this DateTime value, DateTime asOf)
+    public static int Age(this DateTime value, DateTime referenceDate)
     {
-        return ((DateTimeOffset)value).Age(asOf);
+        return ((DateTimeOffset)value).Age(referenceDate);
     }
 
     /// <inheritdoc cref="DateTimeOffsetExtensions.First(DateTimeOffset, DayOfWeek)" />
diff --git a/X10D/src/Time/DateTimeOffsetExtensions.cs b/X10D/src/Time/DateTimeOffsetExtensions.cs
index 977cc60..c1acbbf 100644
--- a/X10D/src/Time/DateTimeOffsetExtensions.cs
+++ b/X10D/src/Time/DateTimeOffsetExtensions.cs
@@ -30,10 +30,10 @@ public static class DateTimeOffsetExtensions
     ///     Returns the rounded-down integer number of years since a given date as of another specified date.
     /// </summary>
     /// <param name="value">The date from which to calculate.</param>
-    /// <param name="asOf">The date at which to stop calculating.</param>
+    /// <param name="referenceDate">The date to use as the calculation reference.</param>
     /// <returns>
     ///     The rounded-down integer number of years since <paramref name="value" /> as of the date specified by
-    ///     <paramref name="asOf" />.
+    ///     <paramref name="referenceDate" />.
     /// </returns>
     [Pure]
 #if NETSTANDARD2_1
@@ -41,9 +41,9 @@ public static class DateTimeOffsetExtensions
 #else
     [MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
 #endif
-    public static int Age(this DateTimeOffset value, DateTimeOffset asOf)
+    public static int Age(this DateTimeOffset value, DateTimeOffset referenceDate)
     {
-        return (int)(((asOf.Date - TimeSpan.FromDays(1) - value.Date).TotalDays + 1) / 365.2425);
+        return (int)(((referenceDate.Date - TimeSpan.FromDays(1) - value.Date).TotalDays + 1) / 365.2425);
     }
 
     /// <summary>