Evans Costner was 18 at the time. His girlfriend, 14. But it comes down to a technicality because he was 23 days too old.
"My son has to spend the rest of his life on the registry," Donna Costner said.
Costner had consensual sex with his high school freshman girlfriend.
"We talked about and decided to do it," he said. "We took all the proper steps, wore protection."
Having sex with someone under 16 in the state of Michigan is illegal.
FOX 2: "Didn't you know that was under age?"
"No, well I knew it was under age," Costner said. "But I didn't think it would be such a big punishment."
Attorney Cheryl Carpenter said Costner did commit an offense - one which he pleaded guilty to.
Costner said he realizes that being on the sex offender registry's implications.
"Pretty much, my life is over," he said.
"Sex offender registry is different," Carpenter said. "That should not be applied in cases where teenagers in high school have consensual sex.
Costner would not have been on the list, except for 23 days.
"Twenty-three days does not make him a monster," Donna Costner said.
That's because the age difference for the Romeo and Juliet Law must be no greater than four years apart. This Romeo was four years and 23 days apart, and the Michigan Court of Appeals ruled this week that four years means four years.
Now Costner will be on the registry for life.
"It's a good law for people that are going to rape little kids and do weird things like that," he said. "Not me."
The purpose of the Romeo and Juliet Law was not to have teenagers on the sex registry list at all - assuming those teenagers were not a danger to the public.
But the issue is whether those teens are true Romeo and Juliets.
"What legislatures do, is they draw lines," said Professor Peter Henning of Wayne State University's Law School. "They picked four years.
"This is what lawyers always argue about. It is called a slippery slope. Four years is the cut off.
"If you are a day over, too bad."
Costner is now 24, has a girlfriend of five years who is the mother of his 1-year-old.
"People are going to look at me weird," he said. "I can't advance in my job."
Donna Costner said her son can't go to school events due to the sex offender law.
"Once the system's got you, it's got you," Evans Costner said. "Even if the mother tries to go in there and say, 'No he didn't do anything, I don't want to see him get in trouble. I was just mad.
"The state will pick it up and take it. There's nothing we can do about it."