Are there any nouns that refer to males AND females without changing form according to gender?
There are nouns which describe character: умница, зануда etc., which describe profession: врач, адвокат etc.
It would have a "ь" at the end, wouldn't it?
I don't think so.
And I'm also having some confusion about the word человек. It means "person", right? People usually use it when talking to an older guy. Would they do the same thing with an older woman? What is the feminine version of человек?
It means person, man, human. It is more often used when talking about a man than about a woman. There is no feminine version of this word. Молодой человек means guy, it is often an adressee. one can say about a woman женщина or человек.
s друга a feminine version of друг? nouns referring to male&fem without changing?
The feminine version of друг is подруга.