something Bill dug up online...
Thank you for the question. According to this Iowa Extension publication https://www.extension.iastate.edu/fores ... elder.html
"The boxelder is a fast growing , wide spreading, short stemmed tree of irregular shape. It is of medium size and under favorable conditions it attains a height of 50 to 80 feet and a diameter of 24 inches. However, it is a rather short-lived tree, is quite brittle or fragile and is of little value. Because of its rapid growth on good soils, it has been planted frequently for shade and ornamental purposes in areas where other trees do not grow well. It is found over most of the eastern United States as far west as Montana, Utah and Arizona. In Iowa, it is found mostly on moist bottomlands and along streams except where it has been planted on higher land".
Based on this information, your tree may be nearing the end of its life span but you also note that the tree looks well. We can't tell you if there is a disease, pest, or environmental problem with your tree based on the provided information. As maple trees mature, some sloughing of bark is normal as the mature forms appear. Depending on the location and conditions your tree is growing in, it may have some lichen growing on it which isn't necessarily a problem either. If you value this tree in your landscape, have a certified arborist out to assess it. Here is a link to our publication that points out keys to successfully hiring a qualified person: http://www.extension.umn.edu/garden/yar ... -arborist/
If you want to learn more about common problems of maple trees, see "What's Wrong with my Plant?" here: http://www.extension.umn.edu/garden/diagnose/