My 7 week old has slightly red hair. how likely is it that he will or won't be red haired as an adult? at what age do you "know"?

Back generations: The inheritance of hair color is not yet fully understood but there are some predictable factors. Red hair is associated with fair skin and freckling so the emergence of all three makes it more likely that a recessive gene (MC1R version) from both parents, neither of whom may have red hair, could be expressed. Both parents could inherit a copy of the gene without having any sign of it.