Qualified

Being able to cross a Gate or one of the Great Gates is said to make you qualified for what's beyond said Gate.

Typically, you are either said to be qualified for a given zone (able to cross at least one Gate to it) or the Labyrinth in general (able to cross a Great Gate)

Labyrinth qualification

The only requirement to qualify for entering the tier 1 zones beyond the Great Gates is to have at least one Potential of 18 or greater.

The average person has a capacity of 15 in any given potential. One person out of 15 will have 16 or more; among those, one out of 15 will have 17 or more, and so on. The highest potential by a normal person is 20.

It's been estimated that about one person in 350 will have at least one qualifying Potential. Until recently, it was relatively hard to determine one's potentials, except by guessing for some (dexterity, strength, intelligence mainly), so the only known method was to attempt to cross the Great Gate and see if you came through.

The modern era has brought so-called Reading arrays, which can be used to gauge the set of potentials of someone. Portable arrays are very imprecise, but larger, more accurate ones already exist. His Majesty's Government is thinking about starting a systematic program of checking for qualified individuals to recruit as Professionals.

Children qualification

In general, children do not qualify for the Labyrinth. The youngest person to ever enter was a 14 year-old girl.

Professionals do not have children in the Labyrinth. It appears to be impossible to conceive in any of the Zones. Attempting to enter the Labyrinth while pregnant is highly discouraged: beyond 2-3 months, the expecting mother will suffer a "spontaneous" miscarriage.

For a long time, it was thought that it was completely impossible to bring children in the Labyrinth, but in 1810, a Professional did enter while on her fourth month without a problem. The child was successfully born in the Labyrinth, with a Professional-type descriptor visible, and his Potentials included a Fortitude of 18, indicating its potential qualification for the Labyrinth. However, the baby lacked a level or Profession (the relevant sections of the descriptor were absent), and the vitals were only 10% of what the Potential listed would warrant. At 8, his vitals are now about 85% of the expected value, and it is widely assumed that he'll get the Organiser Profession when he reaches 100%, which is estimated to be between the age of 11 and 12.

There are only three such "Labyrinth children", aged 8, 4 and 3. They can cross the Great Gates without any difficulty. No children born of Professionals outside of the Labyrinth shows any descriptor, and none have been able to cross the London Gate thus far. Given the numbers of such children aged 14 or above, this is considered "normal" by scholars of the Royal Society, who assume such children are governed by normal rules (unlike the Labyrinth-born ones).