hey im sorry to tell u there is no cure for PKU no matter the age. but this is not a awfull thing, PKU is treatable with a resrticted phe diet and a specail formula. i am 21 yrs old and i have had PKU sine birth though i was diagnosed when i was 2 weeks. im alittle concerend that ur nephew was diagnosed so late i would recomend that u have him see a pku doctor and dietican they will be able to tell u if there are any side effects from no0t being dagnosed and provided the proper treatment. u see pku is a genetic inborn error of metabolism, our bodies are missing the enzyme to break down phenylalanine into tyrosine, there for creating toxic leves of phenylalaine to build up in the brain and this coudl eventally casue brain damamge and other problems like slow motor skill and behaviourl and neroclocial problems. but like i said with a resricted low phenylaline diet and special formula PKU is treatable and u can grow up and have a normal life, for example i graded from highschool 2 yrs ago, i live with my long time boyfriend , im a recepsionist and will be goign to college nextyear. currently i am trying to organize a pku walk a thon to help spread awarness for pku and raise donatiosn for the low phe food products ..also im working on a webiste for pku (http://www.PKUersUnited.piczo.com) so u can see that if the low phe diet and foramla are used PKU is managble and treatable. i wish u and ur family all the best and ill pray for ur nephew that he is well and that it was caugth in time. if u would like to chat further about pku feel free to contact me.. or if u just want to chat in genral feel free to contact me. take care and all the best!