Can older individuals learn new skills, such as playing an instrument, if they have a strong desire to do so but are unsure of how to begin?

Yes, strong desire is a pretty big factor though. It takes more focus the older you get because you don’t quite internalize new information as quickly, so you’ll find yourself having to go through more repetitions. This is why desire is important. It can be, for lack of a better term, “boring.” Doing the reps can become tiresome, especially when you’re older and you have to do more of them to internalize the same concept. If you don’t want it, you’ll quit.