Welcome to the Q&A Forum

In my experience, the date created referred to the page itself as opposed to the entire site. I have migrated about 20 sites and this has not created an issue at all. As long as your domain doesn't change you should be ok. Part of the domain age is when it was first registered, how long it is registered for and whether or not it is an active site. New pages get added to sites all the time. The "date created" is another tag for Google to be able to use to know that there has been an update and there is new content to crawl.

I use Sitecore and it doesn't change the URL if the title is changed. In my case, you first enter the name of the item, which becomes the URL, and then you go on to add the title and content and so forth. (But this may have been an add-on--I wasn't here when it was set up.) If yours changes the URL if you change the title, I'd definitely get that fixed. You don't want a nice outside link to get broken because someone decides to tweak a title and changes the URL! In Sitecore you can easily add aliases however, in case your URL gets changed and you want the old one to still be available (just be sure to add the appropriate canonical--that is a custom field you'd have to have added, or at least it was in my case). There is also a "rename" option you can use to change the URL to whatever you want, again just be sure there weren't any good links to the old URL or if there were, use alias and canonical as above. And as others have said, the title and URL do not need to match exactly, but they should be closely related.