graceful bantams, I have had the same thing, I researched it and it seems that a small number of Marans carry the frizzle gene but most also carry inhibitor genes and the frizzle will just sort of go away as the bird gets older, but it still carries the gene. You can sort of still see it later on in the flight and tail feathers because the look only BARELY crinkly and irregular as adults. You wouldn't notice it if you hadn't been looking really closely for it. I mean REALLY closely.
Everythingjane, let that rooster grow out a few more months. Mine went through some pretty horrendous, gawky, fleabitten looking stages before they started getting really handsome around nine months to a year old.