Teaching Adults

Hello,
I wonder if anyone has any suggestion in teaching English to a mixed classroom of adults from different countries. They range from early twenties to late forties.
Does age matter?
Should they be grouped according to their age?
What would be the best approach?
By the way, they have no basics in the language at all and there are about 20 of them in a class.
What should I do and how do I begin?
I would appreciate some views.

I wouldn't worry at all about their ages. It's a fairly standard sort of mix; I have never had any problems with this. I let people choose their own groupings and sit where they want. If everyone is of one age except for one or two, then the people who are not of the same age may feel a little uncomfortable at first, but they'll settle in. ;-)