Age Difference

My SO is 29 & im 21 (obviously old enough to make my own decisions) but my parents do not approve nor like the fact that he's 8 years older than me. They say it'll never work & a bunch of negative stuff. My SO & I are really happy together, his parents & family love me but my parents & everyone on my side think it's bad. How can I get them to accept it? Any tips or advice? Thanks