I always thought it would be a neat idea if there was a Zelda game that started you off as an old Link.

Ages aren't obviously set in any Zelda adventure, you could have the character age backwards during the game or leap backwards and forwards in time, etc. etc. etc.

If you want a mature Zelda play Darksiders.

If you just want a Zelda with a middle aged link. Why? How would it add to the story? Would this affect mechanics.?
Just slapping a bear on him is dumb unless you have both story and mechanic reason.

Perhaps the game starts in the future of Hyrule and the world has been decimated by some horrible calamity. You begin playing as some old mage/wizard, but as the first part of the game goes along you realize he's actually Link (!).

Zelda is dead in this time line or something. 

This Old Link travels back in time to set things right perhaps. If everything goes according to plan, this future time line ceases to exist. 

Shrugs. To me it seems like it could fit well within Zelda which seems to be all about time travel/alternate time lines/realities. And it would be an interesting way to shake up the "wake up teenager Link! Need to go talk to Old Man Whathisface" beginning that's getting pretty stale. 

The game could still have younger Link in it later on (as you travel back in time). 

I would like a seasoned warrior Link, it would be a good excuse to start off with all basic item versions, like in LBW.
In a note, i would also enjoy a spin-off where you play as Zelda/Sheik. I mean, she is also blessed with the Triforce.

But Tomb Raider, for instance, is like playing porn. It's a good chance to get crap past the radar and yield hilarious results.

What about a female link, but grown up? Like a young mother of two? First non-virgin Nintendo protagonist ever.

I'm not entirely against the idea. But they HAVE, emphasis on the have, to make him badass. And there needs to be a good reason for him to be old. And if they slap in some annoying kids (see skyrim for a how to not do it guide) I'll be pissed. Just a heads up. :D

Bolded: This is the way to do it. Making you play some old man, and then gradually build him up before revealing who he is. Zelda could be dead at the moment, and your mission is to go back in time to save her (before she dies). The problem would be hiding the secret. First of all, they can't reveal it, and secondly it might end up really easy to understand. But who knows, they might be able to pull it of.

Nah, but a young adult (25-30 years) could work.

I would love some kind of spinoff series, but I would rather it be from one of the villians perspective!