The founders of Tinder are fond of comparing their incredibly popular dating app to a bar. Whereas other online dating services are like taking a college class, requiring all sorts of reading and writing of profiles, Tinder is casual and natural. Making a match with the app "is like catching someone's eye across the room," CEO Sean Rad has said.

But sometimes catching that special someone's eye doesn't happen quite that spontaneously. Sometimes you need more than just liquid courage. To enable those matches, Tinder is offering a suite of new features to users willing to pay for them.

The premium features include "Rewind," which allows a user to go back to a profile on which he or she has already passed judgment and revisit the decision to either swipe left (i.e., dismiss it) or swipe right (i.e., seek a match). Premium users will also be able to browse for matches in other cities, a useful feature if you want to book dates before an upcoming trip, opt out of advertising, and "like" an unlimited number of profiles.

But what's potentially controversial is not what Tinder is selling but how it's charging. Rather than charge all users at the same rate, the company is setting different price levels for different age groups. In the U.S., according to TechCrunch, users over 30 will pay $19.99 for the premium tier, while those under 30 will pay only $9.99. In other countries, the price levels vary, but the pattern holds: Older users pay more than younger ones.

The logic behind this pricing strategy is easy enough to understand. Data from OkCupid, Tinder's sister company within IAC, has shown how users' desirability to potential mates decreases as they age. Since older users face a harder challenge getting matches, they're more likely to be willing to pay more for tools that improve their odds.

Charging by age bracket isn't unprecedented. OkCupid also uses age as one of the variables in its pricing equation. Social clubs like Soho House and San Francisco's The Battery often offer discounted membership to people under 30, nominally because they typically don't make as much money, but also because having young, attractive people hanging around is good for business. By the same token, many nightclubs will admit women for free while charging men.