I'm 37 and only been riding Mx for ~3 years, and the two things that gave me (almost) instant results:
1) Factory Connection - revalve. The bike handled better, absorbed all the chop better, and I don't feel like my bike is trying to kill me anymore (kidding.. kinda). Being a beginner/low-low level intermediate on my best day, I didn't think I would be able to tell the difference or notice it, but I couldn't be more wrong. If you do 1 thing to your bike, forgo the pipe, or motor-work and get your suspension done and tuned for you. Note: I'm on a '16 KX 450 w/ TAC. I didn't have to much to gripe about the TAC before, so I ended up keeping the air forks.
2) Lower back extension - this one takes 6-8+ weeks to start to see results, but paired with the suspension, this exercise completely wiped away my lower back pain (I noticed an improvement before the re-valve). This allowed me to stay in the attack position longer and my core was much more stable.
When doing this exercise, forget your ego. I didn't even hold any weight (you see some people holding plates), just used my body. Start off with 2 sets at 6-8 reps per set, then work your way up to 3 full sets. Don't do anymore sets or reps.
Go slow on the way down. Don't use momentum or rock, come to a dead stop at the bottom and pause for a moment. You can put your arms across your chest or behind your back. If you do this exercise right (meaning, you just use your lower back and upper butt muscles), you won't really need much (if any) weight. If you do hold a plate, you will incorporate more muscles and probably rock more and really negate the whole point of the exercise.
Hope this helps some people. 
