I'm 21 and have done a 4 week cycle and 3 week cycle of S1+ with PCT cycles and wanted to know is it still possible to gain lean muscle naturally using supplements like creatine

yea, as long as your diet/routine is good

It's possible.
The biggest and most common mistake people make is eating the same as they were before. If you gain 10lbs of lean mass your BMR is going to increase 60-100 calories, so you should be taking in at least that much more.
It may not seem like a lot of calories, but over weeks and months, it's a huge differance.

So your saying is as long as my diet and training routine is good i could still easily grow lean muscle?

Yes, just realize that it's not gonna come at such a fast pace or as noticeable for some time. I got in the rut a couple years ago where I think I was basically "depressed", when I wasn't on anything (not even PH just any supplement) because I would think my body wasn't looking the same, or wasn't getting near as good of workout. Took alot of friends to help me before what I consider a problem started where I became more of a supplement junkie than a gym junkie.

Just my 2cents,
BOHICA

I agree, great post BOHICA. I also fell into that rut. Its not an easy thing to kick, it got to the point i didnt even enjoy lifting unless i was trying something new, or on something. Every now and again you have to be reminded that gaining muscle, or achieving anything in life is more mental than anything else.