This is an interestingly a reverse of Europe's (effective) policy and on greening the auto-market. Most European jurisdictions
effectively^ tax (and otherwise discourage) old cars wuth a higher rate.
For an example from my country. A 2007 2L Passat is a common old car currently taxed @ €1,000 pa. It quickly escalates to 2,000 as engine size/emissions increase. Passats are decent quality cars with long lived engines, so most of the 10-15 year olds are still alive. For their time, they were average CO2 producers, say 200g/km.
The tax system is designed so that an incremental decrease in emissions substantially decreases annual tax. A 30% carbon saving (say 60g/km saved, in this example) will save you 60% -70% on your annual tax (€600-€800 ish). People buy/drive 12 year old cars for value, and the tax system (by design) takes that value away.
The way to lower your annual tax is to buy a car designed after the new tax regime was designed. The net effect of the policy is that perfectly good old cars are being crushed and replaced with newer, "greener," short lifecycle cars. There's no point building a car that will last more than 8-10 years because tax laws will probably get it off the road by that time. The most economical way to drive is not the old cars, it's cheap new cars.
The real (environmental) question is whether the net effects of building a new car outweigh the case by output of the older car.
Idk what the carbon cost of manufacturing a car is, but the number to beat (for my example, anyway) is about 600 kg co2. My uneducated guess is that it's about even, ie the policy is just another Volkswagen subsidy.