Age Validation Procedure Not Working

The code below is fired from a Worksheet Change Event on cell c18. The cell has a userform calendar control to select Date of Birth. What I want the code to do is check the age at the current date and if it is below 16 or over 25, then show the appropriate message. I cannot use data validation to not allow values outside this age range because there will be instances where a person's details can be added if their age is under 16 or over 25. I just need to alert the inputter in case they are unaware or have inputted incorrectly.

When the message box pops up, if they click Yes then the code should take them to the next cell for inputting. If they click No then it should stay in cell C18 and hopefully pop the calendar back up (I've not tested this bit yet).

The code as it stands brings up the "This person is under 16 years...." message no matter what date of birth is input.

VB:
Sub AgeValidation()
Dim age As Integer
Dim dob As Range
Dim AgeMsgAnswer16 As String
Dim AgeMsgAnswer25 As String

Set dob = Worksheets("Monitoring Form").Range("c18")

[Code] ....