Most people seem to measure maturity as a function of how long it was since you were born and how easily they can get you to do what they say. (Three times now I told that kid to erect the flaming cross on the neighbour's lawn and it's still not done. Goddamn kid's got a lot to learn!)
While age is about the best indicator of physical maturity, I think a good indicator of social/psychological maturity is how easily they are influanced by the salesman (while still being sensitive to the well intentioned efforts of the advisor). There are some situations that reoccur so many times in life we should eventually know what questions to ask, and know when the salesman is getting us to focus on the wrong ones. The mature person should be able to put the issue in a more meaningful frame.
A simple example is 'Buy or Rent'. Not anything specific, well, maybe a widget... just follow along with me. You need a widget. You have decided on the make, model, where to get it, the only question left if buy or rent. If you buy it you make a down payment and the reoccuring fees are much lower. If you rent the widget the payments are higher but you don't have to make the large initial payment.
Enter the salesman. Assume that he wants you to buy the widget. Maybe he gets a bonus if you buy, or for whatever reason he wants you to buy. He can then easily play down the burden of the down payment, How many times do you eat out a week.. cook at home for the next X weeks and it is paid for, and play up the reoccuring payments, Do you really want to have to face a bill of X every month? And it makes sense. If this is the frame issue stays in then buying makes alot of sense.
Likewise if the salesman wants you to rent then he plays up the issue of the down payment and makes the reoccuring payments seem managable. And when he is done talking renting makes sense in this frame of reference.
Many people will make the decision based on the integrity of the salesman. If they think he is not trustworthy they will do the opposite of what he suggests. But remember the indicator for maturity: focusing on the wrong questions. This issue is about whether you should buy or rent a widget. How did the integrity of the salesman become an issue?
In this highly idealized example there are two questions that matter: How much and how long?
Of course it doesn't have to be this formal, but the curves are how much money you have spent over time. The red is if you buy (then maintain), the blue is if you rent. Once you get here the question becomes are you still going to need the widget after the curves cross? If so you will save money by buying it. Solved! And there was no need to speculate on the integrity of the salesman.
This model is also useful for issues of initial investments of time and attention. But instead of starting over every time you encounter a situation like this you can start off with a few speicalized tools then get ready to improvise.