As Cristiano Ronaldo turns 34, how long can he go on?

The Juventus striker celebrated his birthday on February 5

Cristiano Ronaldo celebrates after scoring against Parma on February 2, 2019. AFP

Cristiano Ronaldo shoots on goal in the 3-3 draw with Parma on February 2, 2019. AFP

Cristiano Ronaldo scores the opening goal during the 3-3 draw with Parma on February 2, 2019. EPA

Cristiano Ronaldo reacts after Parma score during the 3-3 draw on February 2, 2019. AFP

Juventus' Cristiano Ronaldo, top right, scores his side's second goal during the match between Juventus and Parma at the Allianz stadium in Turin. ANSA via AP

Cristiano Ronaldo looks on as Gervinho of Parma celebrates with team mates after scoring the equaliser during the Serie A match between Juventus and Parma on February 2. Getty Images

The candles are increasing in number but the flame shows few signs of dimming for Cristiano Ronaldo.

The Juventus striker turned 34 on Tuesday and is now in the latter stages of what has been one of football's most remarkable careers.

On the pitch, the goals are still flowing for the Portuguese, who moved from Real Madrid to Serie A last summer.

How long can he go on?

Well, he's stated before that he could potentially play on beyond his 40th birthday.

He was quoted in 2017 as saying: "When I renewed my contract [at Real] I said I'd still be playing when I'm 41 - it was meant half jokingly and half seriously. If I feel good, without any injuries and I am still motivated, I'll play until I'm 35, 41 or 45. I don't know."

Ronaldo penned a contract with Juventus until 2022 - by which time he will be 37, and teammate Georgio Chiellini backed him recently to play on beyond that time.

“It’s not so much that he comes first to training to make a difference, but rather it’s the way he works: he pushes you to improve yourself," he said. “On top of that, he’s smart: he arrived in a different league and country but immediately tried to understand the dynamics of the city and integrate."

Ronaldo's dedication is well known and his impressive physique is there for all to see.

During a trip to Dubai in January while Serie A was on its winter break, as well as lounging on a boat and soaking up the sunshine he was also seen running through the desert.

He may not be as fast as he was as a 21 year old flying down the wing for Manchester United, and there's certainly less showboating. Instead he's a ruthless machine who will increasingly place himself in the right areas to maximise his effectiveness as he gets older.

How do his statistics compare?

He hasn't stopped scoring this season - and that's the main gauge of where he is as a player. Ronaldo has netted 17 times in 22 matches in Serie A, though he's scored just once in five Uefa Champions League appearances so far.

He averaged a touch under a goal a game in La Liga last season, where matches are arguably more open than in Serie A and the country's defensive ability and style has been ingrained for decades.

One interesting aspect to look at is his top speed, which has reached 30 km/h in the Champions League this season. This is the same as fellow world-beater Lionel Messi, who is age 31.

It is slower than some of the players for whom speed is considered one of their main attributes - such as Gareth Bale, who has reached 33 km/h, and Kylian Mbappe (more than a decade his junior), whose top speed so far is 32 km/h.

Last season, Liverpool's Mohamed Salah clocked the fastest speed in the Champions League at 33.8 km/h, followed by Manchester United's Marcus Rashford with 33.5 km/h.

Ronaldo however was clocked at 34 km/h at the World Cup last summer.

So, although Ronaldo hasn't reached these speeds this time around, he's still at a competitive level when it comes to pace. And context has to be added in - it's not every match that he's going to have the opportunity for a 70-yard sprint.

At what age do legends usually retire?

Much depends on their position, as well as their appetite and physical condition. Plenty of goalkeepers play on well into their 40s, while defenders tend to last longer than midfielders and forwards, given they have less ground to cover and do not need to be so explosive.

At last summer's World Cup, Australia's Tim Cahill was 38, as was Russian defender Sergei Ignashevich. Mexico's Rafael Marquez was 39, while Egyptian goalkeeper Essam El-Hadary was 45.

Zinedine Zidane, one of the finest players in the game's history, bowed out at 33 and moved into coaching. Italian Paolo Maldini, who like Ronaldo remained in excellent physical shape, played on in Serie A until he was 41.

Andrea Pirlo, the former Juventus midfielder whose style relied on speed of thought rather than pace, moved to the United States to see out his playing days before retiring at 38.

Certainly Ronaldo could extend his career with a move to the the MLS, as Zlatan Ibrahimovic did recently, or China. And his absence from international duty since last summer should also help extend his career.

While he may have achieved just about everything there is to achieve in football there is little sign of diminishing ambition.

How did he celebrate his birthday?

The consummate professional, he was at training ahead of Juventus' match against Sassuolo on Sunday.

The club put together a special video in which Ronaldo says the usual platitudes. You can see it below.

It wasn't all work on his big day however, as he later posted a picture on Instagram of his family celebrations with fiancee Georgina Rodriguez and son Cristiano Junior.