Redirect URL:
https://old.reddit.com/login/?reason=lor2&dest=https%3A%2F%2Fold.reddit.com%2Fuser%2F<YOUR_SN_HERE>%2F
Page text:
Log in to use old Reddit
To keep Reddit safe, accounts are required to access old Reddit. Log in, or continue without an account on reddit.com.
By continuing, you agree to our User Agreement and acknowledge that you understand the Privacy Policy.
It seems to be using some cookie system that is bypassing this for the moment. Older machines I have still can use it without issue. But a fresh browser on the same connection will be prompted for the login.
Regardless, it is clear what direction this is going in. Age verification is also being tested in some places.