It is a hard argument to make returning 17 starters and having north of 60 players with two or more years in the program.
I'm not sure exactly what the argument is. You asked if the Gophers would be the youngest team in the nation next year. Not sure if this was tongue in cheek or sarcasm but I said likely no the Gophers would not be. However with the info I provided, I'd say they're still young especially on the offensive side. You countered with returning starters. I don't find those mutually exclusive. You can be a returning starter and still young. If you can't see the difference between a 4th/5th year player and a 2nd/3rd year then we're just not going to come to any agreement.
Again looking at your initial question if we'll still be young. I say yes, especially on offense. Let's look at potential starters.
QB - will be a Soph or potentially a true freshman (unlikely)
RB - could be a Senior but given the injury history of Brooks and now Smith could be a Soph (Ibrahim)
WR - Johnson may go pro but based on his twitter post sounds like he'll be back. So in a 3 WR set it will be 1 SR and 2 SO/FR
TE - no idea. I don't really pay attention to TE in this offense. Let's just say it's all SR
OL - Olson (JR), Faalale (SO), Dunlap (FR), Andries (SO) are pretty close to locks. Depending how things shake out could be Dickson (JR) or potentially Schmitz (SO?).
I count 6-9 starters on offense that will be either a freshmen or sophomores. Seems fairly young to me. If someone wants to do the analysis on other programs to see if that is average/normal I would appreciate it. At 1st glance, defense does seem to be more seasoned. Will take a look later.
I don't really see 2 years in the program to be 'old'. Ideally that player would be heading into their RS Soph season. If you count that as experienced, that's where we're going to agree to disagree.