"I've been told that I shouldn't include any references more that 10 years old, but there are some important papers I feel I should include. What should I do?"
The problem here is with the advice you've been given. 10 years is an arbitrary limit; if you think those older papers are important, then cite them.
When citing other people's work, you have to think about what is the most appropriate source for the point you want to make. For example, if you're writing about the development of an idea, maybe there's a reference from the 1960s that's relevant. Using a more recent reference without going to the original source isn't necessarily a good idea.
Beyond historical significance, some research results from 20 or 30 years ago might still be the best there is. Others will be outdated and no longer relevant. You have to make a judgement based on your knowledge of the field.
So, while you do need to know the current research and you do need to put your own work in the current context, there is nothing wrong with including some older references where appropriate.