Too old
juice can make a difference, but it's unlikely that your juice is too old, depending on how long it's been stored, and how it's been stored.
Really, the best determination (besides the commonly cited 2 year figure) is how the juice looks and smells. If it's super dark, has any sort of precipitate in it and just sort of "seems" funky, well, at that point I'd discard. I'm not sure how fully one can trust a "born on" date in a juice.
I came across some juice that HAD to be 7 years old, or older. It was much darker, and although there was no precipitate, I really had to say, "There is no point even TASTING this juice" although curiosity almost got the best of me.
Some flavors fade over time, some intensify, nicotine may become degraded if it was exposed to too much light and heat. Also, what it is stored in may make a difference, if it's plastic, I'd imagine some seeping might occur.
Just, kind of use common sense, really. If you have juice you want to store for a long time, I'd usually suggest the refrigerator. It may get cloudy and/or separate while cold, but for the most part once returned to room temp and shaken, most of that usually goes away.
The only "premade" juice I store in my fridge is wholesale WTA. But, I stocked up, and I don't use a ton of it, so it goes there. It's been perfectly fine. Away from light heat and moisture but still room temp is usually perfectly fine as well. Etc. Etc.
If a juice tastes harsh or otherwise unfortunate and you know it's elderly, discard it. If a fresh juice tastes that way, it may benefit from more steeping time.
Juice sort of has its trajectory--- you may taste something on the day you mix it, but often that flavor fades away for a few weeks, as it is steeping, then slowly starts to blend and intensify, and will continue to do so for a while, followed by fading (some flavors) or further intensity (some flavors) and the longer it's unused, well, usually the more changes you will see as far as nic.
But harshness can happen by being either TOO young or TOO old, and etc. Also, some juices just are harsh, period .Some folks like that, others want something smoother. Etc.
Anna