If you set the appropriate linux capabilities flag on a binary such as sshd at bootup then unprivileged users can bind to 22, no problem.

setcap 'cap_net_bind_service=+ep' /usr/sbin/sshd

Could even run it as a daemon unprivileged from a home directory with "systemd --user"

That said if you have multiple users and want every user to have their own sshd reachable on port 22 on the same machine you probably want to listen on vhost namespaced unix sockets and have something like haproxy listen on port 22 instead. Haproxy could of course also run unprivileged provided it has read access to all the sockets.