Biceps tendon rupture isn't rare but it is uncommon. The dominant arm is usually injured. Men in construction or heavy manual labor are affected most often. They are often in their 40's and smokers. Nicotine has a known effect on bones and muscles.
It sounds like you have two of the three most common risk factors for this type of injury (age and manual labor). If you are a smoker or use tobacco in any other form, your risk goes up even higher.