Why is it illegal?

It's a question of whether the person has the ability to understand what they are consenting to. Society has decided generally to protect people that otherwise cannot protect themselves. Young children and people who are mentally incapacitated for example. Each state has drawn a line in the sand to say that as a matter of law, a person under age X is too young to understand what they are consenting to. It is an obviously imperfect system, since people mature at different rates, but for manageability sake the states have drawn a line.

In most states it is not illegal for an 18 year old to be with a 17 year old. Many have ages of consent lower than 18, even as low as 15. Also, many other states have laws that exempt people within a certain number of years from statutory rape laws, so for instance it is not illegal in some places for someone up to 3 years older than the minor to have sex with a minor. Again, it all depends on the state.

Because an 80 year old and an 18 year old are both legally capable of making their own decisions. In most states 17 is legal though.

cuz who ever made that law was stupid i find nothing wrong with a 17 year old dating a 18 year old. but they should make one abut a 18 year old with a 80 year old.

A person who is 18 or above is an Adult.

And if both persona are above 18(adults in other words) there is no problem. where as a 17 yr old is a minor

It's because 80 year olds are presumed "mature" and 17 year olds are presumed the opposite. There is nothing "wrong" generally in your examples but because the law is concerned with protecting those that can't protect themselves (i.e. presumably the 17 and under year olds), you have statutory rape.

In fact, it is not illegal. In most states, 16 is the age of consent (unless the older individual is a teacher, coach, pastor or similar).

Actually, in my state (IL) 17 is considered legal. I know this cuz when I was 17 I was dating a 20 yr old & my dad checked it out-he wanted to have him arrested for stat rape...so check your state laws....

what would an 18 yr old want with an 80 yr old unless he or she was a grandparent... little sick dont you think

18 is the age of consent. They had to pick an age and that is the one they picked. I think it should be 21.