No problem. If your concern is the particulate matter, then, yes, banning old diesels makes some sense. They don't have the particulate filters - those started showing up in the 2000-2010 era. However, I would rather see that implemented as tighter standards, and if you can meet them with a retrofit kit, you can continue driving the older ones. We saw this with noise kits for older jets (retrofit kits that reduce the noise to the new standards), and if the concern is specifically emissions, then if you can make an older vehicle meet the newer standards, there's no reason to keep them out. I'm not a fan of arbitrarily destroying old but operational equipment.

My truck is a '97, and I believe the smoke opacity limit for emissions testing is 40% (it's allowed to block/scatter 40% of the light going through the exhaust). I believe commercial trucks of the same age are held to roughly the same standards. That's a good bit of smoke in the exhaust. But until you get into the high pressure common rail stuff (up at 30k+ psi, multiple injections per cycle), you'll get some smoke under certain conditions.

Looking at emissions standards in Europe, a truck from 24 years ago in Europe, assuming its gross vehicle weight is between 1760 kg and 3500 kg, would be allowed to emit 0.25g of PM/km. The same limit for something built since 2013 is 0.0045g of PM/km. We're talking multiple orders of magnitude improvement here.

As a sidenote, HO+NOx has gone from 1.7g/km to 0.350g/km in 2013 (and onto 0.215g/km since then, in 2016), which is often as significant when it comes to desires to reduce air pollution.

Emissions standards change over time. You could get some really polluting cars in the old days, and you can't anymore. Why should we be breathing in the smoke from these old cars from an era where emissions and pollution weren't taken as seriously as now?

The proportion of old vehicles on the road is small. And the last thing most of the people who drive them need is additional expensive compliance hoops to drive through.

For every hipster yuppie driving "muh classic Hilux just like daddy owned in 1993" there a few dozen people living out of the back of a Caprice Classic wagon because they have no better option.