#4 Connie Comes to Town: Connie is newish in town and looking for part-time jobs. She was a waitress "last summer" in California.
#28 The Price of Freedom: Captain McGinty was killed in Vietnam, most likely in '75. Kirk was born after his father's death and is 12 as of this episode. This would date the chronological year of Odyssey at '88.
#29 Jack Davis' first appearance.
#31 Family Vacation Part 1: Jimmy Barclay's first appearance.
#34 Stormy Weather: "I'm fifteen, Mom!"
#50 Karen: Karen Crosby dies around autumn.
#54 Peace on Earth: The Barclays are robbed on Christmas.
#83-84: The Battle: Internet connections and modems are considered new technology. The last time Hal Cunningham was confirmed alive.
#95: The Very Best of Friends: Karen died 'a year before'.
#98: The Visitors: It's Christmas again, and the Barclays were robbed 'last year'.
#99: The Barclay Family Ski Vacation: Donna’s “only 12”.
#108 Isaac the Courageous: Rodney Rathbone is introduced. Lucy says that Rodney is "16 and still in middle school". Apparently she and the other protagonists are as well, so she's probably at least 11, or maybe 10 and a grade ahead.
#113 Suspicious Minds: Connie wants to buy a "brand new used car", and to use it she must be at least 16.
#114: The Big Broadcast: Lucy is introduced as "Lucy Schultz".
#126: Donna and Lucy eat together at lunch.
#133 Cousin Albert: Lucy is confirmed as "in middle school".
#154 Coming of Age: Jimmy enters adolescence. He mentions that the events of Family Vacation were "three years ago".
#181 It Takes Integrity: Curt and Lucy run for student body president in middle school.
#182 The Scales of Justice: Counterfeit money is discovered.
#192 Jack Davis is driving.
#194 Connie teaches Eugene to drive.
#203 Jack Davis has a mustache and is a pizza delivery boy.
#204 Wonderworld: Lawrence Hodges is introduced.
#218 A Class Act: Mr. Everett, who is very wealthy, has a pager and uses a car phone.
#219 Treasures of the Heart: Jimmy says to Donna, "Where have you been for the last fifteen years?"
#254: Katrina Shanks is introduced. She is a similar age to Eugene, and we can assume not too much older than Connie ("The Champ of the Camp, #583").
#267 It Ended With A Handshake: Bernard’s laptop runs either MS-DOS or Windows. Eugene’s floppy with “Katrina, etc.” is a plot point.
Gone…: Connie comments that they couldn’t get in touch with Bernard or Eugene, due to their road trip.
#284: Shannon Everett, whose father is rich, “printed a speech out on a computer”, whereas Courtney Vincent comments that she “doesn’t even have a computer”.
#290 A Name, Not a Number: A wireless phone is a spy gadget.
#294: Stewart Reed Barclay is born.
#299 The Truth About Zachary: Lucy says that she was "9 when her dad (Hal Cunningham) was killed in a car accident".
#300 Eric Myers considers asking Donna out, and is apparently driving by this time, suggesting that Donna is probably about 15 to 16.
#308: Lawrence is an adolescent, and this is his last (regular) episode.
#309 Perfect Witness: Eugene’s desktop computer is in the Mac II series (or a SE/30), all machines manufactured from ’87 to ’90.
#323: June Kendall gets Connie a credit card, potentially implying that Connie was not eligible for one on her own.
Darkness Before Dawn: Jason uses a cell phone — living on the cutting edge! Electric stun guns are newly popular. The laptops Dr. Blackgaard provided to his minions have IR ports. Jellyfish is told to “load his data on floppy disks”. Rusty Gordon, looking at the screen, can’t tell if Jellyfish is “playing games” or doing “serious business”.
#340 Pokenberry Falls, R.F.D: Stewart is a year old. The Barclays are recording the Pokenberry story on some kind of tape.
#351 What Are You Gonna Do with Your Life: Connie tries out different internships.
#375 The Pushover: Jared DeWhite and Sarah Pratchett are introduced; Sarah seems a bit younger than Jared.
#376, #379 Heather and Cody’s parents both have computers with printers.
#380 Connie needs just "one more class to graduate".
#385 Pokenberry Christmas: Stewart is old enough to hold conversations and try to learn to ride a bike. Donna took a psychology course some time ago.
#392 When In Doubt...Pray!: Mandy Straussberg is introduced and in school.
#397: Mandy seems to be obviously younger than in either her last appearance or in the next one.
#398: Jared makes a R/C plane, complete with a controller and working guns.
#405 Connie graduates as valedictorian, and can be assumed to be 18 at this point.
#427 Something Cliqued Between Us: Jared uses the “Compucom” email service.
#431b The Virtual Kid: Alex makes a website, which is considered cool and hip.
#443 Rodney is in high school… with Mandy Straussberg.
#451: Nathaniel’s father is rich after making “FactsBuffet.com”.
Relatively Annoying: Alex is fixated on his handheld video game.
Novacom series: Alex and friends rave about some highly advanced new computers. Websites are ubiquitous. The NovaBox comes out and is a massive market success.
#535: Donna is in a California law school.
Room Enough for Two: Mark Horton is deployed to Raqistan.
Bassett Hounds: Wooton’s cousin lost her money in a “failed dotcom business”.
The Green Ring Conspiracy: A major plot point centers around Dirk’s “Appleberry”. Whit refers to counterfeit money being found “a few years ago”, presumably in Scales of Justice.