Insufficient data. You would have to provide a whole lot more information about your health and fitness history than just your age. Which by no mean alone is enough to be considered significant or an excuse.
Start with the very basics: height, weight, fat %, pre existing heart or lung conditions, smoker/ex smoker. Fitness level. Any recent changes in lifestyle, job, or eating habits? And a very important one, how is your sleep?
Otherwise there could be a million reasons why your short of breadth including something as simple as a common cold.