Depends on what you want to do as a volunteer. Older people need to be aware of their physical limitations (especially when it comes to health) and endurance when volunteering.
An indirectly-related case in point: A lot of people talk about getting retirees (aged at least 55 and above) to be teachers, especially in "easy" centres of learning like preschools. Unfortunately, as a preschool teacher/supervisor, I do not agree. As a person aged 55 and above, how much of stair-climbing can do you in a day, even if it's just one floor up and one floor down? How many times a day can you carry a crying child or a number of them, especially up/down a flight of stairs, before your legs and back give way? How many times can you sit down (either on a low child-sized chair or the floor, which tends to be worse) and get up in quick succession while doing classroom activities? How fast can you run/move when responding to real and perceived emergencies? What will you do during gym class and dance practice? Will you exercise and dance with them, or just stand around, give instructions and expect the kids to know how to do it? I have many reasonably healthy relatives who are aged 55 and above, and some of them were once school teachers, but I will greatly discourage them if they ever want to start teaching in preschool.
---
btw, I stopped working when I was 28 and undertook volunteer work full-time for 2 years before returning to work. There were a lot of early mornings, late nights, running around from home to hospital to another home to morgue to home to crematorium, drug users, depressed peoples ... that sort of thing, so being "younger" and more "energetic" was an advantage.
---
What do you want to volunteer in / as / for ?
I really admire people that volunteer to help other people with little or no compensation financially. I also want to do that however money becomes an issue.