Depends on how strong you need it to be, you could just write the date installed to the registry and check that it is not too old that way, or you could spend alot of time making more complex methods.

There is no such thing as a robust code. At the end of the day, its all binary exposed and it all comes down to and 'if statement' validating whatever criteria you have in mind. If it is for some specific client a time based regedit approach will suffice.