After a 10 year stop from riding awhile back I had the same first ride you just described. Don't worry about speed for now. The good thing is, time in the saddle and distance will increase a LOT the first couple months as long as you go out most days. Ride 5 days a week for a month and you will think nothing of 10 mile rides and will be looking for a longer ride once a week to expand you horizons.