While some of the NPCs will not talk to you sub 50 (some higher, actually, IIRC in the monk epic for example), and some hand ins took place in the planes, I don't think there was an actual "hard cap" that just ate items turned in by a lowbie.
I'm almost positive I've seen the Ragebringer MQ'd to a 30-some during Velious-era (or before, actually as by that time she was 50+ I believe and had an early Willsapper) on the Lanys server. Can't remember her name, she was a paladin who switched mains to a rogue around that time in one of the larger guilds.
Other then that, brief google search:
http://eqmac.com/forums/viewtopic.ph...0dd6d&start=15
"I did this PC side Pre-Luclin on my Rogue and was using Ragebringer at 48. I started working on the quest at 40 (pickpocketing the items, etc). I might have had it sooner, but leveled on my way to finish the quest. Of course, that was PC side, but it was an era before the time EQMac is frozen in."
http://everquest.allakhazam.com/db/quest.html?quest=761
"There are certain epics that can/have been MQ'd to a lvl 1, such as a little lvl 1 Inky warrior who's always sitting in the bazaar on Prexus."