The safety spent the night cramming for his first start, reading over his playbook in the team hotel and asking every veteran in the secondary questions until lights out.
Seven starts for one of the nation's best defenses later, Allen said he feels like one of those veterans as a sophomore. He's not the only one.
Rookies have ascended the depth chart immediately at Penn State, where coach James Franklin - and Bill O'Brien before him - have been challenged to make up for scholarship losses by managing and maximizing young talent. Allen is one of 47 rookies who've played the last two seasons for a team that's been among college football's youngest.
It's not an ideal strategy. But it was necessary, Franklin said, for a team that played every Saturday with well below the NCAA-allowed 85 scholarships.
Counting injuries to a handful of seniors, Franklin had just 44 scholarship players available in the season finale against Michigan State.
''I think it helped for this year,'' Franklin said. ''But at times it was painful last year that we were relying on so many young guys in so many key spots.''
While their inexperience showed at times, the rookies proved they were quick learners.
Allen emerged as one of the unit's better tacklers and arguably the secondary's hardest hitter. He inspired so much confidence in Bob Shoop that Penn State's defensive coordinator has turned most on-field communication duties over to Allen, whom he calls the quarterback of the defense.
Cornerbacks Grant Haley and Christian Campbell both made names for themselves as special teams dynamos. Haley was the team's primary kickoff returner and both were effective gunners on punt coverage, where opponents averaged just over seven yards per return. Linebacker Jason Cabinda became a mainstay after entering to help a banged up defense against Northwestern.
Offensively, receivers Saeed Blacknall and Chris Godwin and tight end Mike Gesicki all factored into the offense and combined for 47 catches for 547 yards and three touchdowns. Redshirt freshman DaeSean Hamilton led the Big Ten with 82 catches.
It didn't take long for Penn State's real veterans to take notice and feel at ease with rookies playing big snap counts.
''I know that I don't ever worry about those guys going in because I trust them,'' junior defensive tackle Austin Johnson said.
That trust and shrinking experience gap go a long way in strengthening bonds between players, Franklin said. But it can be a challenge in a blue-collar locker room.
When Penn State put out its first spring depth chart more than a year ago, it was largely based on seniority with little time to evaluate incumbent players. Later on in training camp, Franklin talked with then fifth-year senior Miles Dieffenbach, who was stunned by the amount of newbies practicing with starting and even second-string groups. Dieffenbach began his Penn State career fifth on the depth chart at guard before earning a starting job as a junior.
''I think there's a little bit in football, a rite of passage,'' Franklin said. ''That you're sent to the scout team for a year and you earn your stripes down there and then kind of come up, where our guys, we didn't really have the ability to do that.''
Offensive tackle Andrew Nelson redshirted in 2013 but not before O'Brien had to pull him back from entering an early non-conference game. Having only been in the program for a few months, Nelson had been practicing with the top two offensive lines. He enters this season as a proven commodity with 13 starts last season.
His has been one of the primary voices in the offensive line room, helping 11 other rookie linemen catch on fast, like he had to. He feels like he's seen enough to offer some leadership.
''It's trial by fire and that's how really great players shine,'' he said. ''Young guys get thrown in there and they do their best and they succeed and that's how you really grow young guys into great players.''
Penn State will continue to try and grow them. Franklin expects four rookies - receivers Juwan Johnson and Brandon Polk, cornerback John Reid and running back Saquon Barkley - to play this season.
Their teammates are just fine with that.