Tea Plants (Camellia sinensis) Time to Maturity

If I bought some tea plants - Camellia sinensis, how long will it be before they are mature enough to harvest, without damaging them?

It generally takes three years for the plants to be old enough to harvest from them. If they grow out of shape in the meantime there is no reason why you could not trim them into shape and use the trimmings for tea.
Just in case you do not know, harvesting for the best tea should be done after the plant has experienced two weeks of no rain and had day temperatures of about 20 degrees Celsius and night temperatures of about 10 degrees.
To harvest, cut the tips with two leaves.
To make green tea from the harvest, steam or heat the harvest right away, then roll and then heat to dry.
To make black tea, roll harvest one half to one hour long, then ferment one to two hours (although another reference recommended three to six hours of fermentation) and then dry.