You could start watching horses being tacked up. It is really not that difficult.Ask your trainer, a good trainer will not have a problem showing you, but ask before or after all lessons.
As for the grooming, they do not require brushing every day.
You may even be able to find a calm quite horse that is a little younger, but I loved my older horses.
I prefer pasture or larger turn outs with a shade/rain cover, and if you are in area that gets snow maybe a 3 sided shelter .
Any horse at any age, can get to the point it needs to be euthanized. I have had some horses that needed euthanized as foals, 11 yrs and then of the Old ones, when their quality of life had diminished , even if I had not ridden them in years and they were simply pets.