What Exactly Is An Aged Domain?

Was does an aged domain mean exactly? To be aged does a domain have to have a site that has been indexed for a few months? Or is it the actual length that the domain has been registered. Because I have a bunch of domains that I have bought years ago that have just been sitting with no site or anything on them.

Would these be good to build on and start blasting links to immediately or do they need to have a site and be indexed for a few weeks first?

I consider the "age" of a domain to begin when it first has indexed content.

"aged domain" is a loosely defined term. I consider domains that are a few years old to be "aged"

The age of a domain is basically how long it has been running.

Starts from the date it was first registered.

Some consider it to be the registered date and others the date from when content is first indexed. I regard it to be the latter.