Startups: Companies that are in their initial stages of business and typically developing a business model and seeking financing.
The message isn't telling you you're ineligible, it's telling you the account you're signed in with has no approved application attached. You don't apply from inside the Azure portal. From the overview: "Every startup joins Microsoft for Startups the same way: by applying through the website."
So apply at startups.microsoft.com first, get approved, and the credits appear in the portal. Reviews take about three business days with the decision by email. If you've already applied, check you didn't use a different Microsoft account from the one you're signed into Azure with.
On the account age, that isn't a factor. The published criteria are about the company rather than when the Azure account was created. Was the account you created in July a personal Microsoft account or a work account? The portal is refusing that specific account, and knowing which it is would narrow whether that's the issue.
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