Held needed in adding "Days Opened" Field in Custom field Edited

[Balakrishna M]

I have to add custom field in my project , which has to tell me the no of days the defect is opened . 

Days Opened = Now - CreatedTime

I have been searching about that ,I read about adding scripted field but which is not available in my jira version , what is the other best way to do it.

Jira version : Jira Service Desk Application 3.3.0

Thanks in advance