I am assuming that you are talking about US Savings Bonds:
Here is a page that talks about maturity dates of US Savings bonds. If They aren'tSavings bonds but are another type ofUS Government Bond
Assuming they are Savings bonds, here is information regarding redeeming of bonds.
How do I redeem my EE/E Bonds?
Electronic bonds: Log in to Treasury Direct and follow the directions there. The cash amount can be credited to your checking or savings account within one business day of the redemption date.
Paper bonds You can cash paper EE/E Bonds at many local financial institutions. We don't keep a list of banks that redeem bonds, so check with banks in your area.
What will I need to redeem a paper bond?
Before taking in the bonds to redeem them, it's usually a good idea to check with the financial institution to find out what identification and other documents you'll need.
When you present your paper bonds, you'll be asked to show your identity. You can do this by
being a customer with an active account open for at least 6 months at the financial institution that will be paying the bonds, or
presenting acceptable identification such as a valid driver's license if the >redemption value of the bonds is less than $1,000.
If you are not listed as the owner or co-owner on the bond, you'll have to show that you >are entitled to cash in the bond.
The treasury direct website also discusses converting bonds, rules regarding using them for education, how often they are credited with interest