One thing that I think music teachers would probably frown on is that I picked up Rocksmith and made more progress with that than practicing chord changes, scales, and Hal Leonard songs. The score for being on time on the right note with the software always adding a few more notes than I can play works really well for me.
Plus I can play it with my daughter.
For me a metronome is not a source of frustration, it probably calibrate my sense of time and is like a wingman for locking into place. Usually it makes warm up efficient, and when my hands are loose I can just walk the neck as I feel.
I've heard the RockSmith critics. I can understand but I felt it's not a bad step, although it's quite incomparable from making your instrument sing. Kinda like driving a car vs Gran Turismo.
All instruments are different though. Guitars require quite a large amount of time to adapt your left hand (neck). It's easy to never make progress there. Bass guitar is a tad easier because you play melodies and not a blend of this + chords, which are demanding in dexterity and stamina.
The frustration, abort, guilt cycle is hard to avoid. Even guys who took lessons as kids have off days. They told us on boards that when they struggle to play, they just take it easy and make it a rudiment day. Stupid patterns at slow pace, just to keep warm.
Do not ocmpare yourself to kids, it's mostly masochism. It's like comparing the speed of a fresh windows 95 install vs a 2 yo one. They have natural excitement and smoother fingers, I believe their brain is just a nasty pattern cruncher and most things end up intuitive the next day. That says nothing about your own ability to learn or take pleasure. <= pleasure which should be the goal.
One question, do you use a metronome ? everytime I struggle, 2 minutes of metronome backed practice suddenly realigns my hand and my ears and everything gets smoother. Not perfect but it helps to get properly warmed up and enjoy the feeling.