The particular base attribute (perception, strength, fortitude, agility, intellect) level; in addition to raising the base damage and block damage of the character also limits the associated combat and other perk levels.
eg.
Boomstick level 1, Strength Level required =1,
Boomstick level 2, Strength Level required =3,
Boomstick level 3, Strength Level required =5,
Boomstick level 4, Strength Level required =7, and
Boomstick level 5, Strength Level required =10,
This may be
interesting reading.