Weapon Familiarity:

All weapons that your class has “access” to, are the weapons your character has “Basic Familiarity” with.
The primary weapon you begin play with will be considered “Familiar” choose one.
All other weapons are “un-familiar”
In game while in use of a weapon it can move from one position of familiarity to another.

If a weapon that you have “Familiarity” or are “Very Familiar” with has not be used for awhile it will drop back down to “Basic Familiarity.”

Un-Familiar                         -3
                                             -2
Basic Familiarity                -1
Familiar                               0
Very Familiar                    +1

(How quickly familiarity is gained or lost will be determined by the DM)
(Familiarity might even go beyond this point, again at the DM’s discretion.)

What this system does:

It removes the aspect of any class not having any access at all to certain weapons.
 It clearly shows the difference between having specialized or simply using a weapon.
It stacks with any other ability that gives weapon specialization.
It rewards players for sticking with one weapon even if a magic weapon of a different variety were
available.

Thus a fighter is neither proficient in all weapons or in three weapons, nor is a wizard forbidden from ever learning how to use a long sword.

The idea of being proficient with a weapon is left as a lifelong process not something learned before level 1.