Yes that formula is useless and no wheres close to what you should be, I'm 54 and hit 187- 189 on just about every ride and can get up to 192.
You are fine unless you have a known heart condition if you stop and your heart rate starts to drop right away you are fine if your heart rate stays in the upper range for a long time you may want to get checked out to be sure.
I say this because a friend till a few years ago who seemed to be in great shape and was very fast found that he had a heart condition he still rides but at a much slower pace and really watches his heart rate he can hit 200 easy, one thing that happens to him is his heart rate will stay up and will not drop very fast to recover, a sign that something may be up.