The Forgotten Realms Campaign Setting is the only source I'm aware of for the feat Create Portal (34). The feat is untouched by errata and has as its only prerequisite the feat Craft Wondrous Item (PH 92-3).
But the Forgotten Realms Campaign Setting on Building a Portal says
Any character of at least 17th level can build a portal if she knows the Create Portal feat and either the teleportation circle or gate spell. (61)
As the feat Craft Wondrous Item has as its lone prerequisite Caster level 3rd, a wizard can take the feat Craft Wondrous Item then the feat Create Portal as his wizard bonus feat at level 5.
Yet he won't be able to create on his own a portal until level 17.
This seems like a long time to wait.
While it's interesting that a low-level wizard could knock on the archmage's door and offer his portal-building skill in exchange for the archmage's spell knowledge (the Wiz5 providing the feat and Wiz17 providing the spell knowledge), unlike many other magic items, the portal doesn't need the Wiz17 to expend the spell gate or teleportation circle during the the portal's creation. Seriously, in the hypothetical scenario, the archmage supervises portal creation, expending zero resources except time (and, perhaps, patience at being stuck hanging around a Wiz5).
Here're the questions.
The Forgotten Realms Campaign Setting is from 2001. The game is in its infancy. Should the quoted text be read as guidelines, as the feat Create Portal has no further prerequisites? That is, should anyone with the capacity to cast either the spell gate or the spell teleportation circle be permitted to use the feat Create Portal? (Perhaps cribbing from an arcane scroll of teleportation circle (9th-level spell at caster level 17) (DMG 241) (4,825 gp; 0 lbs.) is sufficient?)
Alternatively, is there a reason to restrict creating portals to characters level 17 and higher but to give characters the ability to consider for 12 levels their poor and probably pointless choices?
Was the portal creation process updated or expanded upon in later texts?