If waiting has always been hard for you, and your attention has always been restless, that belongs in the anger picture rather than in a separate story.

What the research says

A meta analysis found that young people with ADHD reliably preferred smaller immediate rewards over larger delayed ones, which makes difficulty waiting a measurable difference rather than a character flaw. A prospective study of adolescents found that difficulty regulating emotion predicted later symptoms while symptoms also predicted later difficulty, so the two feed each other in both directions. Neither study says anything definite about one adult, and neither replaces an assessment.

Strength of evidence: one line of research. A single study, or a theoretical account.