wakeboard size
 

I am 5.10 height and 130 pounds, adult male. Is 138cm board too big for me?

Too small. I'd say 140-142

That isn't too small at all. I'm 5'11", 160 and I ride a 139 and like it better than a larger, heavier board. Wakeboard sizes are based on weight and skill level
Im pretty sure a lot of the top pros like Harley Clifford and Cory teunisen ride 135s

I'd say you're good. Most guys your height benefit from riding more in the 140-142 range but you are super light so you are fine.

cory rides a 135 and harley rides a 139. both of them are like below 5 5" though. I would say that the bigger the wake you ride, the bigger the board should be. if the wake isn't that big then can get away with a smaller one. If your on cable I would get the biggest one they have for stability on rails.