I'm like, 9/10 sure the X gene manifests at puberty, but other than that, I'll agree with soren.
Also sicknesses can cause mutant genes to activate. Doesn't have to be stress from life.
@tobiaxI also thought stressors and other experiences triggered it as well. Oh well off to the movies.You are right. See: 90s cartoon Cyclops, maybe other versions. Possibly Havoc.