It actually depends, many people think that 20 is an OK age to get married while some think it is too young. You and your parents, there is generation gap, your parents might have got married very young, thats why they think that 20 is okay to get married, but for you it might be too young because that is how the generation now is.
The only thing that you can do about it is, IF you think you are too young for it and that you are not ready then you have to talk to your parents, tell them about the generation, how it is nowadays that you are simply not ready for it.
It is not worth it to get into a long time relationship ir you are not ready for it. But honestly for me, i think 20 is too young to get married, there is soo much more in life, but as i said depends on thinking.