Here's Jake Peralta's age in Terry in Brooklyn Nine-Nine's very first episode.
The timeline of Brooklyn Nine-Nine more or less follows that of the real world. In season 4's "Coral Palms Pt. 3," a news channel references Donald Trump running for president in 2016. The episode in question also aired in 2016, putting Brooklyn Nine-Nine into a contemporary context, give or take a few months. But even though his character has slowly matured over Brooklyn Nine-Nine's seven seasons, Jake's juvenile behavior makes it tricky to pin down how old the Die Hard-loving detective really is. Fortunately, Brooklyn Nine-Nine gives the audience a few clues as to Jake Peralta's actual age.
In the Brooklyn Nine-Nine season 1 episode "The Apartment," Jake states that he's "only 33," and in season 7's "Pimemento," Rosa Diaz explicitly states that Jake is 38 years-old. Jake also tells Amy he's a Gemini, which places his birthday in either May or June. "Pimemento" aired in February 2020, so assuming each episode is set around the time it premiered, Jake was born in 1981. This also fits with "The Apartment," which aired in early 2014. By the end of Brooklyn Nine-Nine's seventh season, Jake is stated to by 39.
Debuting in September 2013, Jake would have been 32 years old at the start of Brooklyn Nine-Nine, and still very much young, free and single - in his head at least. By season 7, the 38/39 year-old Jake is in a long-term relationship and happily married to Amy Santiago, who gives birth to their first child in the season finale. It’s taken years for Jake to grow up and settle down, and even though he's still a child at heart, modern Jake is at least somewhat grounded by his relationship with Amy.
Andy Samberg was born in August 1978, making him a shade less than 3 years Jake's senior. The actor would've been 35 when Brooklyn Nine-Nine first aired and 41 throughout the latest season. Although Samberg is a little older than his character, he not only looks good for his age, but also for Jake's, and could probably get away with playing a character as young as 30. The practical jokes and constant buffoonery probably help in this regard. Jake's age compared to his nearest and dearest also makes for interesting reading. While he might only be a year or two older than his wife, Jake's best friend, the irrepressible Charles Boyle, is a full decade older than him.
Brooklyn Nine-Nine season 8 is set to premiere in Fall 2020 on NBC.