As an adult, you have different strengths and weaknesses in music than does a child. The best way for you to learn is not the same as the best way for a child to learn, but if you adapt to the way your brain is now, you can learn very well.
A child's brain is more plastic and picks things up faster. It memorizes things faster, and has an easier time with motor skills. However, that brain is not so much better that it puts your adult brain at a fatal disadvantage. You have something that the child's brain does not: discipline. Where the young brain might find it too difficult to keep going when it gets difficult, you are more likely to practice anyway, to find ways around the difficulty, or power through it, or take a break and come back tomorrow rather than just give up forever in frustration. Living an adult life with its challenges has taught you how to keep going when things are hard, so that will be one of your biggest assets as you learn an instrument.
Scales and exercises
Related to discipline is the practice of scales and exercises, which you ought to embrace. Many beginner music books and series emphasize the playing of tunes, because people want to learn music in order to play music. It makes sense. Who wants to just do scales and exercises? However, the one thing I wish I had done when I started music was to emphasize scales, exercises, and basic technique over learning to play actual tunes. I'm not saying to not learn to play tunes, but make them an adjunct to your main study, not the main thing.
This advice is based on my own experience: I learned to play many tunes when I started, but all I could do was recite the tunes. I was like a musical parrot. But once I added scales and exercises (and a little theory) to my practice, my playing technique got better, I gained some ability to improvise, and my playing got more musical. I started to get the ability to make my own arrangements, and learning new tunes became much faster. It was focusing on the basic that made that possible for me.
Scales and exercises and theory are the bedrock. Your adult brain's sense of discipline and working for long-term goals will allow you to focus on them, and you will progress much quicker as a musician.
And, as you show very well by asking your question here, you are well positioned to think about the process of learning on a higher level. Rather than just practice a scale or a piece, you are prepared to ask yourself (and others) questions about how to best practice. If you look at an accomplished musician, you will find that their expertise isn't just evident in how they play, it's also evident in how they practice. They think about how to practice, they experiment with practice routines, they learn from how others practice, and they adapt their practice routines over time to find what works best for them. This is a significant advantage, since it can make your practice much more effective. I claim that an adult's brain is far better suited to this kind of meta-learning than is a child's, so this will be your other great strength.
By applying the strength of an adult brain, you can do just as well as the child's brain. You'll just learn in a manner that fits the adult brain better.