Playing g5 as black, or b4?

I actually thought of g5, but I couldn't see a continuation. Even after the game, I don't see Stockfish lines helpful to understand why g5 is good. The other option is b4, but that also leads to g5. The idea I had was to incorporate a rook lift, which is probably not the right time for a rook lift. So, how can I understand the queenside pawn situation and advance the g pawn? Or is there something else I should have thought about?

You got to look at multiple moves, not just one. What next? b4 is still going to be played.

I have trouble getting past 4. ... d6. Doesn't that lose quickly to 5. Ng5?

Well, since you asked.....

I played a game not much earlier where I should have played d6. I know it means nothing in this game, but I did it more out of training purposes to get that d6 in before Na5. I will deal with that later when I play stronger players who catch me on. I figured I need to get in the habit of d6 to protect the e5 pawn first. 

If that is the key difference in the g5 b4 question, then ok I won't play d6 like that. However, is there anything useful to learn from the position I asked about in the OP? I thought maybe some pawn principles on the queenside and kingside attacking ideas could be learned.

We can always complain about earlier moves, but let's look at the position at hand and decide if it is worth looking at. My opponent didn't catch the earlier moves and it looks like I made a fundamental mistake in not playing g5 or b4. I didn't understand and I still don't how to deal with that position. So, if there is anything to address with that position, let's go over that. I know the d6 was inferior but that doesn't seem to address the g5 and b4 question.

Yes, so Black either ends up a Pawn down with his light squares naked, or goes into a Fried Liver a whole move behind.

Either alternative seems lost.

There is no mate or lose piece after g5.( g5 is a good move though)

21. g5 Ng1

22. g4 Rc2

23. g3 h3 ( You cant sacrifice bishop on h3 because it is double protected with g pawn and kt).

Better move is , b4 then g5. ( b4 fixed rook mobility as she no longer need to protect "a5 pawn", and doesnt lose any tempo.

In general, a forced move without losing tempo and improve in position is first priority. 

I would favor g5 instead of b4. You should be playing on the side of the board where you have the advantage. From that perspective, there were probably some Q-side moves that should have been avoided, instead playing on the K-side.

The only reason I might play b4 would be to prevent Qxa5 in reply to g5, Ra7-g7.

Why?

After g5, shouldn't the a8-Rook enter the game via Ra7-g7?

You might even get the best of both worlds with something like Ra7, Rf6, Qf8 and Rg7.

Yeah, I saw that one.