How long after the booster covid vaccine will my protection begin to diminish? is it by 6 months or sooner than that? is 6 months when it looses most or all effectiveness?

It is after 4 months by recent literature with the third dose but I truly doubt its effectiveness to the Omicron variant. For a healthy young man, I do not think another booster (4th dose) is necessary with the currently available Pfizer or Moderna vaccine. In the last study from Israel, the protection time (?) of the 4th dose is even much shorter.

Infection protection from vaccination -- against COVID or any other infection -- is not a black & white, all-or-nothing issue. Best research so far indicates protection remains highfor around 6 months. After that, protection gradually becomes weaker -- but probably remains strong (especially against serious illness, if not infection itself) for many months, maybe even for a year or more.