Here's some advice to folks who say they can't play:
1. For players who say their timing sucks, practice with a metronome or a drum machine every time you practice or just play for fun. Every time. Your timing will improve by leaps and bounds because it eventually becomes second nature.
If you look at the David Grissom lessons videos, there is a drum machine going that he plays along with. Even he needs a tempo and a beat to play to.
2. Play through mistakes, don't go back. Everyone, including the greatest virtuoso and symphonic players who train for their entire lifetime, hits a clam. Everyone. Hit a clam? Just move on. You wouldn't turn around, go home, park the car in the garage, and start over if you forget to signal a lane change driving to work, right?
3. If it's OK for Neil Young to play simple guitar parts, it's OK for you. Simplify everything. Make every single note count. Maybe you'll start adding stuff to your lines. Maybe not. But one right note, played with a vibe and feeling, in just the right spot, kills.
4. If you stumble playing 16th notes, play 8th notes. If that's a bit complicated, play quarter notes. Too much? There are half note lead lines that sound magnificent. Or play a note per measure. Get the idea? Play the same note over and over if you don't know exactly what to do next. See above comment on Neil Young.
5. Play every single day, even if it's just for a few minutes. The brain and the hand muscles love repetition.
6. Playing scales can be useful, but it can also be incredibly boring and rote. Play some songs. Mix it up.
7. Get together with other musicians who are more advanced than you are, and jam. You'll learn new things, pick up tips, and have a good time. Host the jam. A place to play is always appreciated. If you can't put an electric band into your place, then host an acoustic guitar jam. If you go elsewhere to play, bring the beer. The guy who brings the beer is always welcome!
I have a talented friend who switched from concert flute to electric guitar about ten years ago. He loved jazz, and was trying to learn all this complicated material. A very good sight reader from his orchestral flute playing, he also has a good ear. But he was constantly frustrated. He'd get about two measures into a song, and everything would fall apart. Then he'd stop playing, swear a little, and put the guitar down. He asked me what I'd suggest (why, I don't know, since I'm relatively worthless on guitar).
"Why don't you first start with some simpler stuff and learn some blues," I suggested. After all, so much contemporary music is rooted in the blues, it's a good place to start. Some players stay there and love it.
He took my advice. He progressed from blues to more complex stuff, and along the way he got into classic rock. He's the lead player for a pretty good band and he's in his 60s now.