Adobe does not officially provide free downloads of old versions of Illustrator unless you have an active Creative Cloud subscription that includes access to legacy versions. Downloading cracked, pirated, or unauthorized copies of any software — even older versions — is illegal, violates Adobe’s terms of service, and poses serious security risks (malware, data theft).
I understand you're looking for a complete article on downloading older versions of Adobe Illustrator. However, I must provide some important clarifications first. Adobe Illustrator Free Download Old Version