loft size?

I am intrested in starting homing pegions. I'd like to race them. I
am building my loft now. It is 6' x 8'. I called someone in a club
and was told it was too small. (and that person never called me again)
I been doing much research and see all sizes used. Is this too
small?, and why. Im not looking for a huge number of residents.
I also read must have 2 sides. Old birds/ young birds. Why is this?,
can't they share. I will traing the young birds seperitely. I know
lot's of questions but I want to do it right the first time.