If twice a month is your goal the bike makes no difference. REALLY. Wheels on the couch would work. If you want to get off the couch it will take 4 rides a week. The four rides a week are not excessive if you want to get in shape enough to ride with your son. When I first started riding the rides were not but 7 to 10 miles each, but it was almost every day. The length of the rides increase as you get in shape. You cannot get in shape to ride 25 by riding twice a month. Enough bad news. Now, about the bike. The first bike makes very little difference because you will change bikes as you get in better shape. Just my experience.