Just to reiterate what driftlessregion already wrote. How you ride or train depends on your cycling goal.
If your goal is to get faster for the same intensity level, then you must incorporate interval work into your weekly riding. Interval work being going 100%, so hard you thought you could not go that hard, for short, semi-short time periods. Repeat as long as you can. Best done with a race team or on a racer training ride because left to your own motivation, you never push yourself as hard as your body is able to be pushed. Do 2-3 of these workouts a week. Short and intense. 30-40 miles. 2 hours. Not a big time committment. Try to get 2 of the 3 weekly interval workouts back to back. You are trying to push your body harder. You need to be able to push it when its not 100% recovered. Do 2 interval workouts back to back. Rest a couple days. Do another interval workout. Rest a couple days. Repeat. You can do other rides of easy or medium intensity on some of the rest days. Short or long miles. Or not ride at all. Swim, jog, walk on some of the rest days. But really rest 1 or 2 days a week by doing nothing more strenuous than walking a bit. The hard interval work is the important part. It is enough to allow you to ride centuries easily. Riding short and hard allows you to ride long and medium easily. You do not need to ride 80 miles to build up to riding 100 miles. Two months of interval training of 30-40 miles each will allow you to ride 100 miles easily.
If your goal is to just ride and enjoy yourself, then ride and enjoy yourself. If you feel tired and not up to riding, then don't ride. Go at whatever pace your friends are riding at. Interval work is not necessary, BUT, BUT, BUT some interval work as I describe above will make just riding around more enjoyable too. The interval work 1 or 2 nights a week will allow you to easily ride long distances on the weekend at a medium pace but at a lesser effort elvel. Enjoyable rides will be more enjoyable because they will be less work. You will have the ability to choose how youride your enjoyable rides. Faster like a racer man, charge up the hills to show off, race from town to town and rest a long time in each town eating and drinking and talking, or just ride at a medium or slow speed. Whatever you choose because your body is faster and stronger and gives you the choice. And when there is a headwind, it won't feel as bad because you are faster and stronger and it won't affect you as much. Bike rides are not enjoyable when you are forced to be on the bike longer than you want and put out more effort than you want to put out because your body is not strong enough to overcome the hills, wind, cold, heat, etc. Being faster and stronger lessens the affects of these variables and makes all rides more enjoyable.
Again, don't worry about over training. For 99.99+% of bicyclists, its a myth. Maybe some people experience it. Maybe. I rode 10,200 miles last year and never overtrained. Longest ride of 310 miles in a day. Several 200+ mile days. Many 100+ mile days. Etc. World peace and famine and hunger are probably a higher worry than overtraining.