When writing a will and doing estate planning in general, the age of your heirs makes a dramatic difference in how you plan. This is one reason why it's so important to update the plan moving forward.
For instance, when your heirs are minors, you may want to decide who should be a guardian and take physical custody of them if necessary. You may also want to set assets aside in a trust so that they can get them when they grow up; many people feel it's smarter to leave substantial amounts of money to adult children than to teens and college students.
As you can imagine, your own age when you had your children really sets the stage here. While estate planning is very important at any age, many people really start thinking about writing a will as they get older, perhaps around retirement age.
How old are your heirs at that point? Say you're 50 years old when you write your will. A child born to 20-year-old parents could be already in their 30s by this point. You may feel comfortable leaving them assets directly in your will. However, if you didn't have your child until you were 36, he or she is around 14 years old when you write that will. Now you have to think about trusts, guardians and other such issues.
This is important because people have started waiting longer to have kids. As the average age for women to give birth to a first child keeps climbing, more and more parents will have these complex estate planning questions. It is very important to know what steps to take and what options you have.