The adult beginner has two advantages the child does not: patience and a reason. You are not learning to impress anyone; you are learning because you want the music in your hands. The method that fits adult life is the small one — ten minutes a day, every day, rather than a heroic hour that the week will cancel anyway.
Structure the ten minutes so they do not need a plan: two minutes of warm-up, five of working on one small piece, three of playing something you already enjoy. The point is the daily contact, not the progress per session. Instruments are learned in the gaps between sessions, not during them.
Find a teacher or a structured course for the first months; self-teaching produces confident wrong habits. And record yourself once a month — the phone on the table, one take. The recordings are the proof of progress, because progress is invisible week to week. A year of ten-minute days sounds like nothing until you play the first recording again.