they don't agree

So my boyfriend and I have been seeing each other for 5 and half months now. We are in a long distance relationship, which is really hard for both ends of the story. Well recently I told my sister and her fiancée that I have a boyfriend which they are fine with me having a boyfriend but they are against the fact that he is older than me by 4 years and a different nationality. I'm 20 and he is 24. I knew that they would not like that idea and told me not to tell my parents about the relationships because they would definitely no allow us to date and I would be no longer there daughter because of who I have chosen to love. I've planned to tell my parents after being in the relationship for a year but I don't know anymore.