What is the age of consent according to federal law?
I understand it is 16 years old - is that correct?

How does federal law relate to state law?

For example, some states list an age of consent
that is up to 18 years old.

Which should I go by?

Is it legal for a man 25 to have (consenting) sex
with a 17 year old?

Hello curious369:

As nelson-ga points out below, age of constent for sexual activity is
a state matter, and the laws/rules vary from state to state. As well,
the rules vary depending on whether you (as a male) were planning on
having sex with a female or a male. Let's assume you are asking about
age of consent for a female partner.

There are several excellent resources on the Web that detail what the
exact ages of consent are for the various states. While they all seem
to agree in the most-part, occasionally there are slight differences.
For that reason, I would tend to use the list at Wikipedia (the
information there tends to get updated very quickly as circumstances
change):

Age of Consent (Americas):
URL: http://en.wikipedia.org/wiki/Age_of_consent#Americas
Note: Scroll down to the "United States" section. 

This would mean that the states where it would be legal for a 25
year-old man to have sex with a 17 year-old woman are:

Alabama, 
Alaska, 
Arkansas, 
Colorado, 
Connecticut, 
District of Columbia, 
Delaware, 
Georgia, 
Hawaii, 
Illinois, 
Iowa, 
Indiana, 
Kansas, 
Kentucky, 
Louisiana, 
Maine, 
Maryland, 
Massachusetts, 
Michigan, 
Minnesota, 
Mississippi, 
Missouri, 
Montana, 
Nebraska, 
Nevada, 
New Hampshire (as long as you are not a "person in position of authority"),
New Jersey, 
New York, 
North Carolina, 
Ohio, 
Oklahoma, 
Pennsylvania, 
Rhode Island, 
South Carolina, 
South Dakota, 
Texas, 
Vermont, 
West Virginia

Washington and Wyoming are iffy - see the Wikipedia list for details. 

Other tables that also take male/male relationships into account can be found at: 

Sexual Consent Age Laws (USA)
URL: http://www.coolnurse.com/consent.htm

Worldwide ages of consent
URL: http://www.avert.org/aofconsent.htm

There is one area where Federal Law comes into the mix:

"Federal law forbids crossing state lines or international borders
with the intent of having commercial sex with a person who is under
18, or any sex with a person who is under 16 and at least 4 years
younger than the perpetrator."
URL: http://www.answers.com/topic/age-of-consent

Search Strategy (on Google):
* "age of consent" sexual federal state
* "age of consent" sexual states Alaska Georgia

websearcher

This is regulated by state law, not federal.  I know a great web site
for this info., but I will let a researcher answer.

You may also wish to see http://www.ageofconsent.com/

It seems that the age of consent links are mostly gone, like
ageofconsent.com and that coolnurse.com site. Any newer updated sites
available? Also, most of these questions pertain to straight sex. What
about gay sex? I know it is more iffy, but where can I find concrete
up-to-date info on the subject? Thanks.