Added docs entry for file_older_than function

content/reference/functions/file_older_than.markdown

@@ -0,0 +1,53 @@
+---
+layout: default
+title: file_older_than
+aliases:
+  - "/reference-functions-file_older_than.html"
+---
+
+{{< CFEngine_function_prototype(filename, datestring, option) >}}
+
+**Description:** Returns whether the file `filename` is older than some fuzzy time offset `datestring`. What file statistic is compared depends on the `option` argument. `"modify"` compares the time offset with the last modification, `"access"` with the last access and `"change"` with the last metadata change. `file_older_than` doesn't follow symlinks.
+
+{{< CFEngine_function_attributes(filename, datestring, option) >}}
+
+The function uses under the hood `date --date <str> +%s` from GNU coreutils, located at `/var/cfengine/bin/date`
+
+**Example:**
+
+```cf3
+body common control
+{
+  bundlesequence => { "init", "main" };
+}
+
+bundle agent init
+{
+  files:
+    "/tmp/myfile.txt" create => "true";
+
+  commands:
+    "/bin/sleep" args => 10;
+}
+
+bundle agent main
+{
+  classes:
+    "is_8sec_old" expression => file_older_than("/tmp/myfile.txt", "8 seconds");
+
+  reports:
+    is_8sec_old::
+      "/tmp/myfile.txt is older than 8 seconds";
+}
+```
+
+**See also:**
+
+- Related functions
+  - [`strtotime()`][strtotime]
+  - [`isnewerthan()`][isnewerthan]
+  - [`isnewerthantime()`][isnewerthantime]
+
+**History:**
+
+- Introduced in 3.29.0