Those reason statements are up to four codes that indicate, in order of greatest importance, why your FICO score is not a perfect 850. Depending on the code, they could appear even if the actual scoring impact was tiny, e.g. 2 points.
Individual lenders and CC issuers can set whatever internal policies they want regarding approval for products. Typically the three variables in practice are the applicant's score, the applicant's income, and the particular product being applied for -- though a particular lender might have additional criteria. (E.g. Chase has its 5/24 rule, which can prevent a person with a 500k income and an 840 score from getting a card.) Also considered is how much credit you have already have, from that lender and from others.
So in practice what is often the case is that your score and income and existing credit have together precluded you from approval -- but not a single sub-factor from the scoring model. If a couple factors are given these are likely the top reasons your score isn't high enough.
As far as the two factors you mention....
"Time since most recent account opening is too short". This may well stop having an effect on your score after 1 year. That's the speculation here on the forum. (It's "Age of Youngest Account.") On the other hand being certain that for all FICO models Age of Youngest has a single breakpoint of exactly 1 year -- that's more than anyone can know for sure. And most importantly, what really matters is your score. Some people have scores in the 820s with an account on their report that is 3 weeks old. So you could be approved with an Age of Youngest at 3 weeks or denied with an Age of Youngest of 3 years. Depends much more on your score as a whole.
"Length of time accounts have been established" This is sometimes used to mean Average Age of Accounts and other times used to mean Age of Oldest Account. Both factors could have an effect on your score (if small) even after they become really high. But I am guessing that Age of Oldest doesn't matter much if it is > 20 and that AAoA matters very little once it is above 10 (possibly 8). And as with Age of Youngest, a person could be approved with an AAoA < 1 and an Age of Oldest < 1 -- or be rejected with an AAoA > 10 and an Age of Oldest > 20. Depends on score as a whole.
