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.

Discipline

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.

Meta-learning

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.