Mobile Responsive Sites…

Technology has changed massively over the past 5 years. More and more people are accessing the web via a mobile device.
If you are building a new website today, would you even consider NOT making it a responsive site for mobile and just concentrate on a site for larger screens?
Take forums for example, most are still not mobile compatible.
What considerations do you take when crating a new site?
Is the age range you are targeting your main concern?

See original post by Brian123