Castling Error

I recently played a game at chess.com in which my opponent castled queenside. It is more common to castle kingside but sometimes queenside castling is a good idea. If a player wants to initiate a pawnstorm on the kingside, queenside castling frees the kingside pawns for an attack. In my game, however, queenside castling is a mistake because I have a strong attack on the queenside. My opponent was Clearknighto of the USA who played black. Here are the moves of the game along with my commentary:

1. e4 e5
2. Nf3 Nc6
3. Bc4 h6
4. 0-0 d6
5. d4 exd

I want to open the centre because the black king has not castled.

6. Nxd4 Bd7
7. Re1 Qf6

Black puts his queen on the best square for his king knight. My knight on d4 is attacked twice but it can be defended easily.

8. Be3 a6

It is better here for black to develop his knight or bishop to e7.

9. Nc3 b5
10. Bb3 Qe5
11. Nd5 0-0-0

Black makes a bad move. I have my pieces on the queenside and the black queenside pawns are easy to attack.

12. a4 Qxe4

I want to open the queenside for more lines of attack against the black king.

13. axb Nxd4
14. Bxd4 Qg6
15. bxa6 Bc6

My a-pawn is two squares away from queening. I must not move my knight here because the black queen and bishop can combine to deliver mate on g2.

16. a7 Kd7
17. Ba4 Bxa4
18. Rxa4 Ra8

I am happy to eliminate black's bishop. The black rook is reduced to a defensive role.

19. Qe2 Nf6

I want to check with my queen on b5. Black finally develops his king knight.

20. Qb5+ c6

Black forks my queen and knight. In this case, it is a mistake. Though he is lost regardless of how he plays, he can last longer with Kc8.

21. Qb7+

Black resigns. I can mate on my next move. Black must reply with Kd8. I can then play either Bb6# or Qc7#.

If black plays Kc8 on move 20, the game might continue as follows:

20. Qb7+ Kc8
21. Re8+ Nxe8
22. Qxe8+ Kb7
23. Rb4+ Ka6
24. Qa4#

If black plays Kd8 on move 20, the game might continue as follows:

20. Qb7+ Kd8
21. Qb8+ Rxb8
22. axb8=Q+ Kd7
23. Qc7#

Queenside castling is often a good move. In this game, however, it is not. It is better for black to castle kingside or leave his king in the middle. I am able to launch a quick attack against his exposed king.