With baby boomers outgrowing their midlife crisis years and millennials not yet earning enough money, sports cars sales in the US are starting to go down.

Even though there are still plenty of buyers interested in owning a car that not only goes fast, but looks fast as well, men born between 1946 and 1964 (who buy the most sports cars) are already moving past their peak spending years.

"Boomers are starting to age out of sports cars," said Eric Noble, president of CarLab, a US-based consulting firm. "When you get in your 60s, comfort becomes more important. Sports cars are not going away, but the market will get smaller."

Noble goes on to say that Gen Xers won't be helping sports cars sales much either since there are fewer 35 to 50 year olds than before. As for millennials, they're not earning enough money yet to even buy an entry-level Mustang, let alone something like a Corvette Z06.

While Ford will still probably sell over 100,000 Mustangs this year, through July, about 25% of them went to car-rental agencies and corporate fleets, according to IHS Markit.

In 2016, about 40% of Mustang buyers were baby boomers, which is down from 50% in 2013, as reported by Autonews. Of course, models such as the Chevrolet Camaro or the Corvette are experiencing a similar decline with sales down 11% and 14% respectively this year.

Jessica Caldwell of Edmunds said that this lifestyle shift could be happening because people no longer see Coupe models as being cooler than a four-door saloon or an SUV. Plus, with luxury brands such as Porsche or Mercedes-Benz selling multiple sporty SUVs, buyers can make more practical purchases while still ending up with a car that's fun to drive. She argues that a car that "fits someone's lifestyle and is still sporty is a better option than a true sports car."

This trend is very evident when looking at Porsche where Macan sales have gone up 30% this year, as the model is now the automaker's best seller.

"Boomers are coming out of pure sports cars, but they're not willing to sacrifice pure driving," explains Branden Cote, AMG manager for Mercedes-Benz USA. "The idea of a sports SUV was incomprehensible 10 years ago. They're not giving up spirited driving; they're going to a different type of sporty driving."