What are the best ways to ramp up aging using magic?

Question

What are some of the most effective ways to accelerate the aging process via magical means?

Answer 1

Given that you cite Book of Vile Darkness, which uses bestow curse to effectively age a character, I would understand that you want some way to physically advance a character's age (e.g. so they can become an adventurer or the like). The ethical, metaphysical, and legal of this in your game world are probably beyond the D&D rules to define, but there are various effects in official 3.5 sources which will do what you want in some way.

Spend time on a plane with slower time

A planar trait known as Flowing Time refers to planes where time moves at a different rate relative to the Material Plane. What you want is to find, or create, a plane where time moves more slowly, so that you can live entire years and return aged. According to the SRD under Planar Traits, Time:

Flowing Time

On some planes, time can flow faster or slower. One may travel to another plane, spend a year there, then return to the Material Plane to find that only six seconds have elapsed. Everything on the plane returned to is only a few seconds older. But for that traveler and the items, spells, and effects working on him, that year away was entirely real.

A few examples:

• The Far Realm (Manual of the Planes p.211), where one minute is equal to zero time on the material, so you can age years in an instant. However, the Far Realm may be highly dangerous.
• Dal Quor (Eberron Campaign Setting p.95), where time passes at one tenth the usual rate. It was once coterminous with the Material Plane so you could physically just walk there, but canonically there's currently no way to reach it except in dreams.
• A random demiplane with unique traits

The advantage is that you will really age both physically and mentally, so you'll gain all the benefits; i.e. you aren't just polymorphing a kid into an adult body, you're actually learning the skills and such relevant to being an adult in D&D.

Be breathed on by a time dragon

A time dragon (Dragon Magazine #359) has a breath weapon which is a line of ravaging time. It ages the target one year for each age category the dragon has, no save. It also deals a point of Constitution damage (Fortitude half), but that's recoverable with bed rest, as long as you don't get reduced to 0 Constitution.

Aging Touch spell

The spell aging touch appears in Dragon Magazine #350. It's a level 3 Sorcerer/Wizard spell which deals 1 point each of Strength, Dexterity, and Constitution damage. (Fortitude negates) As a side-effect, it ages the target by one age category. The effect is temporary, however. The exact duration is not clearly stated, but is implied to be 1 point per day. Only the body is changed, and you don't gain any benefits. It's not the optimum solution in most cases.

Time travel

According to Dragon Magazine 350, time travel is not possible in any 3.5 product, but may be possible by some deity-level things like artifacts, portals or divine intervention by a god of time. However, if you can find a way, you can do this to age up a character. See Time Travel at the Forgotten Realms Wiki for various methods.

Suppose you want to age ten years. One solution is to go back in time ten years, then just live ten years; the other is to age ten years, then go back in time ten years.

Bestow Curse

It was mentioned already in a comment, but Book of Vile Darkness has a variant which ages the target.

Invent something else

If you're the DM, you can just invent something. The kid falls into a time portal like that one Deep Space Nine episode, and now they're a grown-up. If you're not the DM, anything you come up with has to go through the DM, so you try to negotiate something.