This week pay particular attention to the elderly when you're making notes of people you see in your writer's notebook
As an exercise, try listing least a dozen ways to suggest someone is very old. Then scroll down and see some others that you may want to note as you're observing.
oversized nose and ears
amount of hair (many women's hair thins as they age too)
color of hair
condition/thinness of skin
quality of vision
pants hiked up
condition of hearing
quality of voice
attitude or outlook
where they are on Saturday night
Half of the above are mine and half from "Funny, you don't look 75" in What If?: Writing Exercises for Fiction Writers by Anne Bernays and Pamela Painter.
(There's also a revised edition in hard back of What if? but I haven't seen that one yet.)