What does it mean for a savings bond to mature?

It's been over 20 years since I have had my savings bonds. I have 2 that originated at $50 and 2 at $75. How long does it take to "mature" and what does this mean? How much taxes do I have to pay on them if I cash them out? I am thinking about cashing them out to help pay for college.
Does this mean it will no longer draw interest or I will be penalized for not cashing it out?

You can go to www.treasurydirect.gov to find out the answers to any/all questions you have about your U.S. Savings Bonds.

Once at the homepage go to the Quick Links for Individuals section and click on "EE/E Bonds In Depth".

Example: To find out the value of your bonds click on the "Tools" tab, then click on "Savings Bond Calculator". Click on "Get Started". Enter the necessary information.

Also, you can look in the section titled "Research Center" on the left side of the same screen as the Tools tab.

1. You can click on "Tax Considerations" for tax information.

2. You can click on "Product FAQ's. When that page comes up click on the question "What is the Education Savings Bond Program".

3. You can click on "Rates & Terms" for information on:
Interest earning life, Original maturity for paper bonds, Tax advantages.