Is it possible to an individual developer to invite another developer to manage apps on iTunes Connect? I developed an application for my friend who has an individual developer registration, I have got a simple developer registration without individual enrollment. 

Is it possible to invite me at the Apple App Store to manage this application? or we need a company registration?
Only Company / Organization accounts can add additional developers to its team. As stated under the Enrollment Selection page, in the Individual account section:

Individual Development Only
You are the only one allowed access to program resources.