In theory, this connection is doable. In Zurich HB, the train to Munich leaves from the underground station. This means, you can take the escalators on platform 10 to go two floors down. That’s not much of a hassle, not even for senior citizens.
If you want more transfer time, how about taking the bus at 05:50 from Horw, Seefeld? By doing so, you will reach Zurich HB at 06:50 already.