I did a bit of googling around, and the general impression I got was that there's no such thing as over-ripe, because it's not a fruit, it's a stem. At worst it'll get stringy. Shouldn't be any harm at all in cutting it back, but I'd leave a few leaves on the newer-looking stems so it has something to photosynthesize through as it grows back.

To deal with an overgrown rhubarb, what you should do is dig up its roots and split them into multiple chunks, then replant them. I'd suggest doing this in the fall.

Note: no kind of expert (my first, tiny rhubarb crown is hibernating at present, and I've never got to the point of picking any) so the usual caveats apply.

Not an expert either, but I concur with Skud's general impression. As a child, we ate wild rhubarb all the time. The choicest bits are the bright red parts nearest the end of a shorter stalk. The really long stalks will lose their color, but not the tart sting that we love about the plant. The fibrous-ness of the stalk is about how thick it is and how close to the ground. Think asparagus.

I am new here, so forgive me if I am asking something odd.

Is it possible to share a photo of this plant?

I am just worried as growing up I lived near a lake with plants like this, of the height you describe. And while it was a relative of rhubarb, it was poisonous. The leaves though were tougher and thicker and had little spiny bits on underside. So a photo would let folks confirm the identification.

Michelle: you're right. It's burdock. Because yeah, too tall, and it has thistles. Though from what I've read it sounds like by "poison" what is meant is "strong diuretic, small amounts might work when a diuretic is medicinally called for."

Isn't burdock root a common vegetable in Japanese cuisine? Yup! Google concurs – it's commonly pickled and you've probably had it in vegetarian sushi (it's the crunchy yellow thing). Wikipedia also mentions a dandelion and burdock drink that is popular in Britain and which I think I've actually had at one point in my travels. Looks like something to add to our list of crops!

In case anyone else has burdock show up in their yard: wear gloves when removing. And a thick shirt. Like stinging nettles, it has prickers with irritant in them, and it CAN go through a t-shirt. A branch swung around and slapped me on the back, and I now have a rash where it hit along with a light scattering of hives all over my body.