I'm 39, and a fairly decent pianist. I learned a bit of guitar when I was younger, but just recently started learning guitar/uke more seriously.

I'm keenly aware of the skills that I spent hours and hours practicing that are now second nature to me on keyboards (such as scales, chords, names of notes) that I need to learn for guitar. Intellectually I understand how things work on guitars, but in order to get decent, I need to start putting in the time to practice playing scales, learning the fretboard, and even just teaching my fingers how to move in certain ways.

And it's not any harder to do this stuff than when I was a kid - in fact, in some ways it's easier. But it takes time and dedication. I have to keep reminding myself that I am actually making a ton of progress. But the tiredness / busyness can make it difficult to put in the time.