I've seen it vary from a person with 0 cards and only AU accounts pull off a 15K CSR app last week, another post in approvals for Amex 15K w/ AU only accounts, and so on...
It varies by profile but, I would say most of us generally find the key to getting there is to push the CLI buton as often as practical until the CL breaks through the barrier.
You bring up a good point by mentioning AUs. I'd rather have data points from people with no AU accounts, as that artificially inflates your credit age.
To chime in on the AU accounts, underwriters don't look at them as artificial credit. They're considered for credit cards and loans.
For me it was a Discover Card in 1999 with a $13,000.00 SL , Filled out a written Application I picked up at a Sears store.
back then I had Amex Gold Charge card (1983), Green Charge card, Optima card, Simmons Bank card Citibank Visa, Providian Bank card, Mervyn's, Macy's & Chevron gas, Unocal 76 gas.
The Discover and Citibank CC's .. just fell off my Bureaus in the last year The rest were gone years ago.
with the exception of The American Express Gold Card, which I still have to this day Member Since '83
I really only remember the limit on the Discover. As I used it a lot to grow my business. back in the day.
Best "Examples" of the cards I held.
My first 10k'er was my Citi AAdvantage card. Started at $8500 and after about 60 days was able to SP CLI it to $10500. My CFU was my first card to start above 10k at $11700
My first ever credit card was my PNC Points back in ~2006. I was denied on it originally (no history) but after buying my first car and using a PNC loan, they asked if I wanted to apply for a credit card. I told them I previously did but was denied (I don't recall the lapsed time... months maybe), so they said let me look at that. They came back and approved me. I believe it started at $3k and I was working a job making somewhere between $8-10.50/hr. I've never asked for an increase, but I think a couple years later after continual use I eventually got sent a surprise Visa Signature card (must have crossed $5k CL) and now it sits at $12.5k CL. I now don't use it except for auto Netflix payment, so I'm not sure if it could go any higher.
My second credit card in 2014 was the BoA Cash Rewards Visa. It was an automatic Visa Signature offered by the Penn State Alumni Association, so it came with $5k CL. It only has auto'd up to $6k so far (BoA must be stingy).
I started getting more credit cards since 2018 (about 6) and they all have had >$10k starting CLs except my Chase Freedom (see sig). I've also never asked for a CL for anything.
My first was the Chase Sapphire Preferred. Started at $5k when I got it in...2013? My credit profile at the time was like a 13-year old's beard: thin and patchy. Despite that, the card grew over time to $14.7k through limit increases and account combinations, after which I had it upgraded to the Reserve.
My first initial CL of $10k was the Amex Blue Cash Preferred at $10k on the dot. I had several accounts already in the $10k+ range by then, however.
I've only had 1 card that ever exceeded $10k, and it was after a house fire in 2005 when I had insurance money to burn (and buy all new stuff). I apped for a new card that had a SL of $5000 and by the time I was done with it in 2007/2008 it had grown via auto CLIs to over $16k. Once the insurance money ran out and the 2008 recession hit I stopped putting more than $2k or so on it a month and the CLIs stopped. This would have been about 20 years after I started using credit, though with never requesting a CLI or putting a lot of spend through cards I never had the occasion to grow one past $10k other than that one time.
I don't have that card anymore (CLDed it a couple years ago to $2k when money got tight and then closed it entirely a few months ago). Now I have no cards over $10k, and probably won't for a long time, if ever. I just don't have the disposable income to spend enough to trigger auto CLIs into the $10k range and I never request CLIs.