DateTime format

Question

I have a datetime in my variable  (datetime i am selected from three dropdownlist and i dont want any connection between these dropdown just display 31 days,12 months and 50 years that i showed in my project and i take that datetime to a variable now.),

 

Now I want to check weather the date is valid or not.

 

ie,if i select 31-02-2017 actually i dont want to check year where it is leap year or not also 

 

when i select this date into my variable i just want to show an exception .

 

How can we use isdate function for this Problem. 

 

Anyone Please help me..

 

 

Thanks in Advance