I've been of the opinion that you should only tell someone of your sexuality if that sexuality directly affects that person. If you are going to be still living in your parents' home and bringing home lesbian/bi partners into their home, then you should tell them. However, if you are bisexual and not acting that way at all at home, and keeping your relations external to the home, then you should keep it to yourself.
In my case, I'm 40+, married for almost 20 years with two kids. I have known I was bisexual since I was 15. The only people I've told about my sexuality is my wife and a few select medical professionals. I never told my parents or my kids since I've never done anything homosexual around them. It's never affected my relationship with them and there would be limited benefit to anyone by telling them. However, if I were to split from my wife (divorce or death) I would likely explore my homosexual side more publicly, and in that case I would tell my kids and/or parents.