I'm 49 and have always wanted a bike. With the gas prices being so high, I am considering buying one.
I'm 6'4" and weigh 240. I've been looking at the Victory Vegas and also the Honda VTX1300.
I'm wondering if I should start out with a bike this large or not. I have sat on smaller bikes and they didn't feel comfortable because of my height.

Any suggestions?      

It is always better to start on a bike with a smaller engine size and get some miles under your belt before you buy one of the big boys.  But, because of your height this may not work for you.  Sit on as many bikes as possible.  I would try the vulcan 900 and Honda 1100 (stopped making these in 2007)for size.  I ride the Shadow Spirit, gets between 57 & 63mpg depending how I ride.  You can try the Shadow, but you may find that you are to tall for it.  I am 5' 8".  Out of the two you mentioned above your best bet will be the 1300.  Another thing to keep in mind is to look at used bikes.  You can usually pick one up with low miles for several thousand less than new.    

Make sure you take the MSF riding course.