If he returns to Goodison it will be FOR his age and experience, not in spite of it.
Think about it. Jags and Barry have both been dropped to the bench. It looks like Jags will be leaving in the summer, Barry less certain but he's not getting longer than another 12 months at the very most. We're now a team with several young players, and hoping to blood a few more. Koeman also knows though that he needs to strike a balance, that the Lookmans and Davieses could benefit immeasurably from the example, advice and mentoring of a Wayne Rooney. This is part of what Koeman means by "making the team stronger".
You've also got to look at it from Rooney's point of view. He can go to China and earn silly money. There's probably American clubs who could double whatever he'd be earning at Everton. If he returns, it won't be for an easy ride and a nice wage packet. It will be for a new challenge, and the chance to give something back to the club that he still loves.
This may be an old debate, but the situation is different. There are three questions to ask :
-- Are Man United prepared to let Rooney go ?
-- Are Everton willing and able to put up the money that it will take to sign Rooney ?
-- Is Rooney ready to quit Man United, and if so, would he want to come to Everton on the terms being offered ?
There are no definitive answers. We can't trust what we read in the press, and anyway, Everton's priorities may change in the next 3 months, and so may Man United's. But we're closer now to being able to say yes to each of these questions than at any time in the last 14 years.