One way to look at estate plans are as a view of your current financial situation. When you create an estate plan, you review what you have and determine how to distribute everything, should you happen to pass away shortly thereafter.
That means you should change your estate plan when your financial situation changes greatly, such as when you get married or have a child. Whenever you plan on having much more or even less going forward, you know it is time to change your estate plan.
That you will need to change your estate plan eventually, is no reason to think you should not get a plan now. You do not know what changes will happen or when they will happen. You also do not know when you will pass away.
An estate planning attorney can advise you on creating and then updating an estate plan to meet the changes that occur in your lifetime.
Reference: Cleveland Jewish News (March 15, 2018) "Wills should be updated when situations change."