It's perfectly fine for a 7 year old boy to wear Luvs diapers or any other diapers when they need them.
Some kids have incontinence and need to wear diapers all the time and others have disabilities that require lifelong diapers and some kids need to wear diapers for bed wetting.
No matter the kids age or no matter the age of the person who needs diapers, the diapers should be worn when needed.
There should be no shame in wearing diapers, no matter your age.