It's not really matter of age (you're 20 - a women, so let's leave behind cases where age do matter, being underage).

It's not really a matter of age. That's a personal thing when you feel ready for sex. You can be 20 or you can be 30. If you don't feel like doing it - you should not.

However, as one person above mentioned, you might want to observe yourself because you should be comfortable with your body when looking at yourself.