Having a 7 year old channel is no big issue, but I'd say instead of completely deleting or unlisting videos, IF they're still related, I'd give them a better thumbnail and title, and treat them as a bit of history.
If I ever end up in the about page of a channel, which is rare, and about the only way someone will see how old your channel is anyway... if your oldest video is from a few months ago, and your channel says started in 2010 or something, it might make me curious briefly, but many channels started long before actually publishing.
I don't even mind subscribing to channels that have videos that are 10 years old with a bit of a gap in between, what you're uploading now is more important, but I think having a bit of a historical archive, if it's still aligning with your focus, is kind of nice to have. But of course if they're personal archive videos that you made for family and now you want to take your channel professionally, make those private. PewDiePie started his channel as way to send video messages to his girlfriend long before he took YouTube seriously.
But no one is going to pay much attention to the date of the channel unless they go to your about page, and that rarely happens.
