Just switched from MTB to Road bike

Hi,

I have been following this group for several weeks and have learned a lot. I
have been riding a MTB for many years for exercise and just bought a Trek
1200 to spice up my riding experience. It worked.

I am 50 years old and with my new bike am interested in setting a goal. I
have decided to attempt a century ride in late October. I had been riding
30-50 miles per week on the MTB. That has increased to 75 miles per week
since acquiring the new road bike. My questions a Does anybody have any
advice on how to train for this goal? and... What is a SAG in an organized
ride?

Thanks in advance
Jay