Stages of Senior Aging. I see a lot of people answer "She is Stage 3" or "She is at Stage 6" What are the Stages?

What you're referring to are the stages of dementia and not "senior aging." Two totally different things, and I've personally never heard of any particular stages for senior aging, other than young, middle age, old and very old.

For those not necessarily dealing with dementia there is also the clinical frailty scale

https://www.physio-pedia.com/Clinical_Frailty_Scale

https://www.agingcare.com/articles/stages-of-alzheimers-disease-118964.htm is a good resource.

Also here http://tinyurl.com/bdhns62w

However, since each dementia journey is individual, the stages are only a very broad guideline.