This will depend largely on three things (and none of them are your age - age discrimination is illegal): Your credit score, your income, and your debt-to-income ratio.

Go to any local bank or credit union, not a national outfit, and ask for commercial lending.

They will help you monitor your credit and provide you with suggestions on how to improve the score.

I know of a few credit unions that will go up to 80% LTV with decent rates, but none in those markets.

If they can't follow directions- DENIEDIf their application is incomplete- DENIEDIf they don't earn 4x the rent- DENIEDIf the don't have ID or their ID is false- DENIEDIf there are 12 income tax lien collections (true story)- DENIEDYou can add on a layer of a minimum credit score, but in my experience enough good people took a hit from the recession and are playing catch up.  

In the private lending industry, plenty of lenders will lend to you as long as the deal makes sense, you have a decent credit score and you have a down payment to bring to the table. 

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

Start talking to local credit unions.

Much appreciated  Actually, be careful with that I used to have a rooming house and a lot of A lenders won't consider any rent at all if rented by the room, some credit unions will consider the rent but be careful as this is one that can hurt more than help.

The thing with Jumbo products is that each lender can make up their own rules - which result in a variety of qualifications that vary from lender to lender.For your specific example under today's conditions (8/8/2022), a $3M Purchase Price at 20% down will get you the following: - With a 740 Credit Score: 6% interest with about $200 of lender credit ($6000 in lender credit if you have an 800)- You will need 18 months of reserves (PITIA of the new property x 18)- Likely 6 months of reserves for the departing residenceLike others have mentioned, you should shop around for Jumbo products since some lenders have opportunistic terms that are dependent upon their investors at the time.