it seems to be a bug in the Firmwareversion 1.06, F-OHT-DC-1004-231: The Max-HR is not calculated 220-age but always 200 independent from the year of birth. The Max HR canīt be set manually, only 5 individual zones can be set manually. This can be done in % of Max HR or absolute in HR.
It would be fine you have to set the zones in percent of HR max. (or the anaerobic treasure, I would prefer) only one time. When HF max. (or anaerobic treasure) changes, you only have to change this one manually and than the zones in absolute are changed automatically because of the relative setting.
Best regards, have a nice weekend