Jumbo Mortgage eligibility

Has anybody gotten declined for a Jumbo mortgage loan because you have a short credit history? I moved to the US 18 months ago through Amazon relocation. When I try to get a pre-approval for a mortgage, I hear that they would be able to give loan only till 741K conventional loan limit. Higher loans would be treated as jumbo loans and they say I’m not eligible on the grounds of credit length although my income and assets are good enough for it. Has anybody managed to work this through? Are there other lenders who can provide such mortgages ? Is it a matter of better negotiation ?