Yes for the actual schizophrenia, but you can have a gene and be pre dispositioned to something yet never actually get it, so if you are an identical twin with the same DNA as your twin, then you would have to have the gene. That is 100% with gene in identical twins whether both actually diagnose with overt symptoms or not.
Schizophrenia develops in boys/men most often between ages of 16-24 unless it has changed statistically in last 10 years.
Right, but that means that environment plays a part too, because not all those with the gene develop it.