Yes it's normal for a 12 year old boy to wear diapers for babies.
A lot of 12 year old boys like to wear baby diapers or wear diapers in general and that's okay.
There are thousands of people in the world who enjoy wearing diapers and even enjoy dressing like a baby or toddler.
I'm an adult now and I still wear diapers and I almost fit into Pampers size 7 diapers but mostly I wear adult disposable diapers that fit better.
Still though it feels so good to put a Pampers size 7 diaper on because it really makes me feel like a toddler.
You're certainly not alone in wanting to wear diapers at 12 years old or beyond and there's nothing to be ashamed about.
I gave up the toilet almost 8 years ago now and have been wearing and using diapers full time since then.
Diapers are the best underwear and diapers are also the best toilet to go potty in.
I love wearing a wet disposable diaper as it feels very good.