What do I do next if my return status says "printed"

Printed means that you have chosen to print and mail your return. You can find steps to print and mail using the links below, depending on which version of TurboTax you used to complete the return. 

https://ttlc.intuit.com/replies/3401713

Can this be changed if "printed" was selected by mistake?

Yes. For instructions on how to switch from mail to e-file please click the link below.

How do I change from mail to e-file in TurboTax On ...

I mailed in my taxes last year, yet when I just checked, the status is still listed as "printed". What would be the reason for my mailed-in taxes not having been "accepted"?

Mailed returns don't get Accepted or Rejected.  That is only for efiled returns.  Turbo Tax will always say Printed or Ready to Mail.  They don't know when or if you actually mailed it and the IRS doesn't tell or update Turbo Tax when they get your return.