I honestly have no idea. I seldom remember my dreams, but it seems that mostly I'm observing what's happening and don't "see" myself.
I don't see myself either but, in some dreams, I am aware of the limitations that age has brought on me, such as being able to run fast or climb stuff, while in other dreams, I seem to have no age-related limitations. In some dreams, I am a (young) student in college, while in others I am someone with more experience.
I dream all the time, but don't recall having any sense of my age in them. I probably will start, now that you've mentioned it.
For me, it varies, even in the same dream. Sometimes, I am young, and my kids are still little kids, but the next moment, I am telling myself in the dream that I can’t do something because I am 78 years old now. Most of the time, I can run, jump, climb, and all that stuff like I did when i was young, so it seems like my age and disability just catches up with me now and then. It is the same with my parents. I can be dreaming about doing something with my mother, and my “other voice” interrupts my dream to remind me that my mother has been dead for about 35 years now, so she can’t be running around in my dream.