NEW YORK — People are living so long these days that you might decide that your 90th birthday would be a good day to draft your will. Bad idea.

Whatever your adult age, it's wise to have a will. Go to a lawyer as soon as you can and write a will, or update the one you have if it's more than three years old.

During your lifetime, you probably will accumulate more wealth than you had ever expected to leave to your heirs, thanks to all those 401(k) and IRA funds. That's all the more reason to put in writing just who will inherit your assets.

Simply engage a lawyer to draft a will that states your instructions for how your wealth is to be distributed. You sign it (usually in the presence of witnesses) and you put it in a secure but accessible place. Officials of your state will see to it that your intentions are carried out, through the public process called probate.

More than mere wealth may be at stake. Only if you have a properly executed will or trust can you appoint a guardian for your children or make special provisions for an aging relative or a handicapped child or a significant other.

And here's another reason to have a valid, unshakable, up-to-date will: No family situation brings on more stress than dividing up dad's or mom's estate after a parent dies. One academic study has shown that when no legally binding instructions were left behind, arguments among the heirs were four times more likely to occur.