So... if that is the case for you as well, I would pay the mortgage off according to the requirements, but not more than that. And I would instead start working on creating investments.
Of course, as you might already know: investments are volatile. Stocks are volatile and bonds (obligaties) also, although a bit less than stocks. So if you start investing, it's possible that you will see a reduce in value of your investments if the markets tank. However, keep at it. If you put money in diversified index funds, at some point the market will recover and so also the value of your shares will go up again.
I would focus on low-fee index investing. The Dutch companies to do that with, are Brand New Day, Meesman, Binck and DeGiro. Each of these offer decent index funds and ETFs for investing. Binck and DeGiro offer also a lot of other options, but I would steer clear of those.
I would also check whether you or your wife still have "jaarruimte" or "reserveringsruimte" ... these are Dutch words that mean that you still have some money that you can set aside in a tax-friendly way for retirement. This blogpost explains it well, in Dutch. If you have the option to set aside money in such a tax-friendly way, then this money will be a tax deduction for this year, meaning that you can deduct the money that you put in from your income, and see a much lower tax burden in your highest tax bracket. (So, if you're in the 40% tax bracket, then if you put in 500, you'll see 200 of that returned to you; if you're in the 52% bracket, then putting in 500 means you'll see 260 back next tax season).
Brand New Day offers a retirement account where you can put in these sums of money and invest them. Meesman doesn't, unfortunately. DeGiro does offer it too, but the fees may rise in the near future (they're going to add a mandatory "robo-advisor" and will ask an as of yet unknown fee for that). So personally, I'm with BND for this

PS. I just read this book: "Miljonair met een gewone baan". It came out October 2017 and it's a nice introduction to the whole field of saving money, investing, reaching financial independence in the Netherlands. Maybe you can borrow it from the library? There's also a Dutch book called "Je geld of je leven", which can be found here for free. It is focused on saving and spending less and it's based on the American book "Your money or your life"; but Dutchified.
PS PS. Mannnn... is there a lot to tell about this Dutch retiring stuff or not? So ... the one other thing I wanted to tell you, is that you should also find out how much you've already saved for retirement. You probably have some AOW-rights already, plus you've probably already contributed money to pension plans or pension investments at work. Find out how much that is. This money will help you to pay your expenses once you have reached official retirement age (70 or so?). So this is good money to have, even when you can't use it when you're 40 or 50 or so.