All Americans should volunteer to do a year of community service. The government should not mandate the year of service but each person should do it because it would help them grow and help the society at the same time. The age of eighteen would be a good age to start.
In theory, it is a nice idea, but I think if you were to analyze the costs of organizing this, and the costs of educated people taking time out from their studies or productive career activities, you would find that the costs would greatly exceed the benefits to society, and would be a bad idea.
I think it is unwise to assume all Americans should do a year of community service. I've been working since I was 15 1/2 years old and not once in that amount of time (15 years) have I been able to take a year off, not even while I was attending college. Trying to volunteer for a year would drag me further into debt, so I'm completely opposed to this idea.
Americans should not be conscripted into any sort of government work. The most the government can ask of us is that we pay our taxes, and even that is a bit much to ask sometimes. The second we start restricting people's time is when America is truly no longer a free country.
Community service should be voluntary. It is also used as punishment for crimes. People shouldn't be forced to do it if they don't want to. Most adults have jobs, and don't have the time to do it, or have children to care for. It's great if people do it, but why punish someone that hasn't done anything wrong?