Cristiano Ronaldo celebrates his 36th birthday today.

The Portuguese legend has achieved so much in his career and he's still going strong as he approaches his forties.

Ronaldo wrote an emotional Instagram post earlier on Friday.

He wrote: "36 years old, unbelievable! It feels like it all started yesterday, but this journey is already full of adventures and stories to remember by. My first ball, my first team, my first goal... Time flies!"

"I’ve given everything I could, I never held back and I’ve always tried to deliver the best possible version of me. In return, you gave me your love and admiration, your presence and your unconditional support. And for that, I’ll never be able to thank you enough. I couldn’t have done without you.

"As I celebrate my 36th birthday and my 20th year as a professional footballer, I’m sorry that I can’t promise you 20 more years of this. But what I can promise you, is that as long as I keep going, you’ll never receive less than 100% from me!"

Ronaldo's career in football has been remarkable.

But not even the Portuguese legend predicted he would still be making his mark on the football pitch at the age of 36.

Last year, Ronaldo was asked by Canal 11 what he thought he would be doing at the age of 35 as a kid.

Ronaldo responded, per the Daily Mail: "I thought I was going to be a fisherman in Madeira.

"This never came into my mind. I wanted to be a professional football but I didn't think I was going to win everything I've won."

Ronaldo has managed to surprise himself.

At 36 years old, he is still setting record-after-record and is still playing at the highest level at Juventus and Portugal.

It wouldn't be a surprise at all to see him still playing when he reaches his 40th birthday.