Caring for uncircumcised son

So mom's, I'm very confused right now.

So on my side of the family, I grew up with my mom and brother, we're always sharing everything to eachother, literally no matter what it is.

So my brother recently seen the doctor for a problem his had an idea of since he was 16, didn't think it was a real problem and that he will "grow out of it", but his 20 now and in university, still a virgin because of this and his realised his not going to grow out of it, so the doctors said its phimosis and because his at this age now, the usual route of treatment won't work and his getting referred straight to surgery for a circumcision.

The doctor also said usually kids are diagnosed with this and his surprised my brother came so late, my brother asked my mom how come she didn't know and she said she had a "feeling" but had noone to ask as she was a single mom (tbh I think even though she was a single mom, if she had a feeling about it, she should've spoke to the doctor atleast).

So these years, this has really took a toll on my brothers mental health because he said he "couldn't do anything with it" even by himself, and because of this, if he ever has kids then he will circumcise them (BTW we come from a country where that's not even a thing, and we live in a country where its not done unless there's a medical reason, its really rare here).

So here's my confusion, I'm a mom of 2 boys, 4 years old and 4 months old, I've been advised when bathing my boys to never pull the foreskin back, I can injure them, but if I don't do that, how would I know about phimosis? Or is there an age where its encouraged to pull back and only shouldn't be done to babies?

This whole thing has made me realise I don't know anything about male problems and I should really educate myself, because my partner even seems clueless even though his had a penis his whole life (uncircumcised too).