Is it normal to not be able to make friends?

Depends on your wants, if you don't want friends or have little desire for social interactions...sure

If not, then it is a skill after all. Just put yourself in more social situations. People are always more friendly than you think :^)

I'm the same way. I have no friends and find it difficult to make them.
That being said, I wouldn't want many. Maybe one or two and that's it. I think thats how many most people have anyway.

Making friends is a social skill and something you do with another human. Your definition of a friend might just be more strict than other people's, or maybe it isn't and the people around you are just not very friendly. Whatever the case, hard doesn't mean impossible.

For some people it can be harder to make friends, I totally understand :)