Is the caster level of an item a prerequisite for crafting the item?
Say for example an item needs the spell Bear's Endurance
A 2nd level spell, you can cast at 3rd level as a wizard.
But the item's caster level is listed as 8th level
Can you make this item before you are an 8th level wizard?
The short answer is "No."
The caster level listed for an item is not considered a "requirement", except in the case of some items which specifically list it as such in the "Requirements" section of the item's entry. For example, to make a +X weapon I think you have to be caster level 3X or something like that. Ironically, some of the blandest, most boring items (weapons and armor) have this drawback and some of the strongest, most broken ones do not (Belts and Headbands, etc).
Some DMs will house rule it to be a requirement anyway (I do that). But even if you do make it a "requirement", there's a rule that says "you may ignore a requirement by upping the DC to make the item by +5" so even if it is a "requirement" by house rule, it's still possible to actually get around it mechanically.
By RAW, a level 5 Wizard with 5 ranks in Spellcraft, the Craft Wondrous Item Feat, and a +4 Int mod will get a total of +12 to his spellcraft skill checks. For him to make a Headband of +2 Intelligence, he needs to make a spellcraft roll of 5 + the caster level of the item, so 5 + 8 or 13. If he rolls a "1" he makes it :) and that's without spending any other feats on crafting, like skill focus(spellcraft) for example.
Of course that assumes he knows the spell "Fox's Cunning", if he doesn't, he can still try to make the item, he just has to up the DC by +5 (the penalty for not meeting the requirement of knowing the right spell), and thus he would then need his skill check to hit an 18, so he needs to roll at least a 6. If your DM houserules that the caster level counts as a requirement, then he'd need an 11, because he's trying to circumvent TWO requirements now, and the penalties stack. (5 + CL of item + 5 for not knowing Fox's Cunning + 5 for not being 8th level = 23, that minus his +12 spellcraft skill bonus is 11, so he needs to roll an 11).
The only prerequisites for an item will be listed under Requirements. You can overcome any requirement by adding +5 to the craft DC for each requirement that you wish to overcome. The only exception for this is the actual Craft item feat itself.
The other exception is for scrolls, wands, staves, and potions. You have to be able to cast the spell to create any of those items and you cannot use the +5 DC change to overcome that.
Caster level is not a prerequisite : it is the difficulty for the skill check to create the item (actually 5+CL), and the difficulty to dispel the Magic Item powers.
The only items for which Caster level is a prerequisite are Weapons, Armors and rare Wondrous item. In either way, those prerequisite can be overcome by a +5 difficulty to create the item.