Your boy is perfect!!
Otter has a GIIIIIIIAAAAAAAANNNNTTTTT head. He was born with a slightly big head -- 36.25cm and by 8 weeks it had grown to 44 cm. Seriously. That's the truth. When the pediatrician looked at what the nurse had written for that (and she checked it 3 times!!!) his eyes buldged out and he immediately started feeling all over Otter's head with a look of worry. He simply couldn't believe his head could be that big with nothing wrong. Right freaked me out!

But he said every seemed fine and we'd just see what happened.
It continued to grow like crazy and has always stayed well off the upper end of the charts. However, it has followed the normal curve shape that all centiles follow -- which means it has slowed at the right pace, just remained big. Now, at 2.5 his head is somewhere around 53cm. He can fit, barely, into a large size hat for BOYS (not tots), but can also wear a size small for a MAN!

He's 2!!
But you know what -- he's fine. Better than fine. He's crazy smart. They moved him into Preschool 6 months before the age they normally would because he already knew everything all the kids in Pre-School knew. He remains super advanced with just about everything. Big heads house big brains.
As long as the shape is normal and it stays on a general growth CURVE (centile matters less), then he is fine.
The funniest thing about Otter is that his big head sometimes gets the better of him. When he's learning new motor skills, you can tell he is at the mercy of that big head -- it throws him around!

He's so top heavy that it can be hard for him to learn to compensate sometimes, which is quite funny. He'll be running at full speed, turn a corner, his head won't coperate fast enough and you can see it start to pull him over.
Here's some pics of Otter to compare for you. The first is at about the same age as your boy now. The second is more recent. Still has a giant head!
https://i758.photobucket.com/albums/xx223/TigerLady_Otter/14d7460b.jpg
https://i758.photobucket.com/albums/xx223/TigerLady_Otter/6a6c9389.jpg