I'm not really sure of the answer, but if it was me. I would approach my own bank about this one. If you have been banking with them for a while, they are more open to taking chances as you do have a history with them. A small business loan may also be an option, but you may want to save that one for later
Lenders make their decision based on credit score, income, existing debt, the amount you wish to borrow, and whether there will be something used to secure the loan (e.g. an auto or home loan involve the bank owning the car or house until you pay the loan off). Business loans can be based on additional factors, such as an impressive business plan. Length of history with a bank can also matter I imagine, as others suggest.
Note that I separate income and existing debt, rather than combining them as DTI. A homeless man with almost no income might have no debt and therefore an impressively low DTI, but no lender will give him a dime because of his low income.
If our OP wants to improve his credit score (one of the things the lender will look at) I can direct him to a place on the forum he can do that. He uses the phrases "very thin file" which he seems to be confusing with Age of Oldest Account. AoOA is important, but it is completely different from what makes a profile thin.
Ceratinly he should tackle making his credit reports and scores as good as possible in the next couple months.
If he describes his annual income for the last two years, current monthly income (last two months), existing debt, and whether he'd be securing the loan in any way, the other folks here might be able to advise him. I have never taken out a real personal loan before (or a business loan) so I can't comment about what's involved there. I can help with the score piece.