Do we reach a certain age where we shouldn't
exercise?

there is no age limit for exercise, the more you do it, the more you are fit and chances of living longer

since you have not provided the options here i   am going to give you general overview about hormone.hormone are actually the part of endocrine system in our body and produced by the endocrine glands. the hormones act like a chemical messenger   within human body. once produce by the glands they   travel through the blood stream and reach at specific or target tissue and organs   which result in control of our body function. the hormones are specific in their work and work on only the targeted tissue or organ   . with the of hormone endocrine system regulate the heart rate , metabolism, our mood and   growth as well as the development and even the sleeping cycle etc. they actually are the messenger for body cell and organs .

age might have something to do with behavior depending on the age because not everyone who is the same age acts the same like 2 year olds could have bad behavior but some won't.

i hope this : )