Lewis Hamilton and Kimi Raikkonen believe age won't be a problem for Fernando Alonso upon his Formula 1 return next year.

This week, it was confirmed the Spaniard, who turns 39 later this month, will be back on the grid in 2021 at Renault, the team where he won his two F1 titles in 2005 and 2006.

Some though have wondered why, at a time when most front-running teams are promoting youth, would the French manufacturer go in the opposite direction?

"I would imagine there are pros and cons on both,” Hamilton replied when asked about that on Thursday in Austria.

“Experience definitely counts for a lot and when you are working with a team like Renault, every team is pushing to develop to move forwards and evolve so experience can help the team move in the right direction so that will definitely be a bonus for them.

“I don’t know what it’s like to be 40 yet, so I don’t know how it is physically challenging. I have no doubts that Fernando can be in great shape," he added.

"The bonus for me is that I was the second oldest and now I’m going down to the third oldest.”

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The current oldest driver in F1 is of course Kimi Raikkonen, who turned 40 last year, and he says there are some benefits from having plenty of years under your belt.

"I'm sure it's not like it was when we were in our 20s," he said. "But I think generally the whole sport has changed a lot since those days, and this year has been pretty easy because we haven't done any races except one.

"I wouldn't say the training has changed. If anything, it's probably less because when you're comparing to almost 20 years ago - everybody's a bit smarter as to what needs to be done, what not to do, what is helpful and what can actually be harmful.

"I think as long as you feel you are capable of doing what you expect to from yourself, it is just a number.

"As soon as you feel it is happening a bit too fast, and obviously that will come at some point, then I think whatever you do, you can't move time backwards."

With Renault still set to be a midfield team for 2021 at least, another key question some have raised is whether Alonso has the motivation for a challenge like that which now faces him.

But asked about his return, Fernando's new teammate Esteban Ocon revealed he certainly isn't wasting any time.

“It’s great,” he told Formula1.com “Of course Fernando is very linked to the brand and if you look at the success he had with the team, it’s for sure fantastic, but we need to build something new with him coming now.

“He has great experience and I’m pretty sure he can bring that to the team and make the car evolve, and he’s very, very motivated. I’ve had him on text yesterday, or before yesterday, and he’s very keen to come back.

“We just chatted about the opportunity there is in these next years and how the field is close at this moment, so I think there is a good chance of doing well if we work well.”