Here's a stat: since 2006, there have been 1,861 International League players with 250+ plate appearances in an IL season.
Rooker's 2019 K-rate is 20th highest out of 1,861. That's really, really bad. No one with such a rate has ever succeeded in the Majors.
Of the top 100 highest K-rates, a few players did go on to some success, but at catcher and middle infield (mainly Tyler Flowers, Danny Espinosa, Jorge Alfaro - all with lower rates than Rooker and far higher defensive value).
So the issue isn't Rooker's age per se - the issue is that his current approach cannot work in MLB, it is completely impossible. So at age 25, he needs to make huge adjustments in order to have a chance of success. That's why age is an issue.