Viking hat help!

hi there,
I’m making this hat for my 2 y/o son…and this pattern is for a 3-9 mo baby --so I’ve increased the # of casted on stitches…I just wonder, when it says to knit until 5 inches long (b4 the decrease part), should I extend that length it for a 2 year-old hat, and by how much?

pattern is here:



Probably by a couple inches anyway. I know someone will come up with a link to a chart for hats, or generic pattern, but I don’t have one.