One of the problems with mathematics teachers and resources

I'm playing the devils advocate here - so bear with me.

I've been looking at the age problems used in all algebra courses.

For example: Mary is three times older that Dave.  In 12 years Dave will be one year younger than twice Mary's age.  How old are they both?

I know someone is going to ask, 'why is this useful?  Couldn't we just ask them how old they are?'  And they will have made a reasonable point.

So I Googled, "Why are algebraic age problems useful?" and got:

The purpose of age problems is to determine the age of the people in the equation.

Really?  So the purpose of driving is to drive?  The purpose of eating is to eat?  The purpose of learning to count is so you can count?  Crikey.

Mathematics educators need to provide FIRST and foremost, the reason that this is useful and give practical examples.  The point of learning is not to help facilitate more learning.  Okay, in some cases it may be (developing automaticity for example) but not in regard to reasoning.

But what's the big picture baby?  What's the end game?  Why should I learn algebra?  When will I ever (!!!!) need to calculate someones age based on the crazy data provided?

Now, I can answer the 'why do I need algebra?' question as there are solid reasons (another post). But I'm still struggling with the application of the age problems.

Someone help me.  Give me a real example of the usefulness of the type of mathematics used in age problems in the real world.  Please.