It say me datetime cannot be converted into int.
Kindly help me wiyth script
It appears that you are looking for a difference in seconds between 2 dates. If this is so then you don't really need to divide the difference by /60/60/24/365. The difference between 2 datetime values is still a datetime, you cannot divide it by an integer. To get what you need, use datediff function instead:
You can read the answer to this question, it has a pretty detailed explanation about datetime math.