If you don’t like green tea because of its bitter taste, you probably did not brew it correctly. A good cup of green tea should taste more sweet than bitter. Green tea contains a lot of antioxidants, and some components attribute to the bitterness and some components attribute to the sweetness. Therefore, in order to bring out the sweetness and suppress the bitterness of your green tea, you need to know how these components work when interacting with the water temperature and the steeping time.
Water temperature is extremely important for making a good cup of green tea. The water temperature usually falls between 165 F and 175 F. The reason green tea requires a lower water temperature is because hot water will quickly extract caffeine and catechin and these two components will bring out the bitterness of the tea whereas theanine and amino acid are pretty stable components in any water temperature which yield the sweetness of the tea. As such, you need to adjust the water temperature to control the bitterness to ensure it will not overpower the sweet taste.
Steeping time is another major factor that makes your green tea tastes bitter. Normally japanese green teas do not need to steep more than 1-2 minutes and chinese green tea do not need to steep more than 2-3 minutes. The longer you let your tea infuse in the water, the more caffeine and catechin will be extracted from the tea leaves, hence your green tea will taste strong and bitter.
In short, water temperature and steeping time goes hand in hand when preparing green tea. If you are using the right temperature but steeping the tea longer than the instruction, you will end up with a bitter taste and vice versa.
One final note, not all the green teas use a low water temperature. For example, the japanese green teas like Genmaicha, Hojicha and kukicha or the Chinese green teas like gunpowder and Chun Mee, require a higher temperature because these teas are made to enjoy the aroma as much as possible, so a higher water temperature is required to extract a full aroma.