HOUSTON — Miguel Moll knew the risk of rape when he was thrown into a Texas jail in 1989 after joyriding in a stolen car.

Then 17, he was placed in a holding pen in Houston, and an older inmate said of the teenager, “I got this one.” The comment sparked the first of many fights Moll had while behind bars.

“The mentality you have to develop very quickly is either that of a wolf or that of a lamb,” he recalled.

A generation later, the federal government has adopted guidelines intended to prevent prison rape in part by separating young offenders from adult inmates. But four years after the rules were supposed to take effect, they are proving difficult to adopt in the nation’s crowded jails and penitentiaries.

Since 2012, states have been working to meet the standards set forth by the Prison Rape Elimination Act, or PREA, which was partially inspired by the 1996 death of Rodney Hulin, an undersized 17-year-old inmate who hanged himself in Texas after his requests for help following repeated rapes by adult inmates were denied.

Texas sheriff’s offices said separating the two populations has been a challenge because of overcrowding and steep financial costs.

“It’s a big logistical headache,” Brazos County Sheriff Chris Kirk said.

The law was also supposed to provide for better staff training, improved reporting and investigation of all sexual assaults behind bars and more money for research.

In 2011-12, an estimated 4 percent of state and federal inmates and 3.2 percent of jail inmates reported experiencing one or more incidents of sexual victimization by another inmate or facility staff, according to the Justice Department.

The rape-prevention law “is a valuable and important act, and we take it very seriously,” said Ryan Sullivan, a spokesman for the Harris County Sheriff’s Office, which has about 150 youth offenders at its jail in Houston. The facility holds more than 9,000 inmates.

The Harris County Jail was cited in a May audit for not housing 17-year-old offenders apart from adult inmates. Elsewhere in Texas, Dallas County is spending more than $11,000 per week to keep at least 60 juveniles separated from adults at its jail complex.

Like Moll, Art Medina was incarcerated at 17 in Texas. He was later sentenced to life in prison in 1985 for his role in a fatal Houston-area carjacking and spent 15 years in solitary confinement after seriously wounding an inmate who threatened to rape him. He was paroled after serving a total of 26 years.

Now in their 40s, both men have returned to the prison system as volunteers to help adopt the PREA standards. Medina said in the past inmates felt like “nobody cares about them.”

“That culture has changed. People are being held accountable,” he said.

The nation’s 7,600-plus prisons, jails, community-based facilities and juvenile detention centers are being checked on their compliance with the law. So far, only 12 states are in full compliance, according to the Justice Department. Thirty-six other states said  they are working to comply.

Still, the department said in an email that it is sees “evidence of a very substantial effort nationwide” to satisfy the new standards.

The age separation has been especially complicated in states such as Texas that prosecute 17-year-olds as adults. Advocates said some facilities still question whether the federal mandate applies to them.

In many jurisdictions, one of the biggest barriers is summoning the political will to make changes, said Brenda Smith, who was a member of the National Prison Rape Elimination Commission, which helped develop the standards.

States that do not comply face losing 5 percent of their federal prison grants. County jails and local lockups are usually not included in the determination of whether a state is in compliance. Locally run facilities have no risk of losing federal money unless that funding is directly tied to a state contract for jail services.

Smith, a law professor at American University in Washington, D.C., said that means local authorities can only be held accountable by public criticism or lawsuits.

In Michigan, the prison system faces federal and state lawsuits filed by prisoners who allege officials failed to adequately separate offenders ages 14 to 17 from adults, resulting in sexual assaults.

A Wisconsin legislative report concluded in July that the state’s prison system was not splitting up the age groups. And an American Civil Liberties Union survey in North Carolina in 2014 found that none of the 60-plus county jails that responded appeared to be in complete compliance.

Those findings have renewed calls for the states that prosecute 17-year-olds as adults to raise their age of adult criminal responsibility to 18. Those states include Texas, Michigan and North Carolina. Sullivan, Kirk and other Texas jail officials said they would be in favor of raising the age.

Efforts to raise the age failed in the last legislative session in Texas, but advocates plan to try again next year, said Elizabeth Henneke, policy attorney with the Texas Criminal Justice Coalition.