How often should I change my oil? (New to bikes)

Hey everybody, I have an '82 Hondamatic CM450A. I changed the oil last May when I got it and my grandpa told me that he only changes the oil on his Honda once a year. Well I'm nearing 2000mi since that oil change and I'm starting to get a bit paranoid. A friend of mine who rides an 80's Yamaha told me he changes his oil every 1000mi.

Also, I don't know if its just my paranoia, but within the last few weeks I've been feeling like the engine has been a bit more "clattery" if that makes sense. I know there's something you're supposed to do with Honda's regarding valve timing maintenance or something, but I'm just not sure what or how to do that.

I hope I haven't done anything to my bike.

I didn't find the right solution
References:

http://www.motorcycleforum.com/101-general-motorcycle-discussion/114384-how-often-should-i-change-my-oil-new-bikes.html

Product Marketing Video

U should do it once a year or every 15k kilometrs