Can I exercise too much?
Sure you can. There is such a thing as ‘chronic cardio’ where the amount of exercise you do can actually have negative long term consequences on your health.
Although in my experience, those I meet who are chronic exercises are often aware of what they are doing and are driven by something else rather than the pursuit of optimal health.
Another quote I recall from a runners forum:
I run to add life to my years not years to my life