City were knocked out of Europe's elite competition in the round of 16 via the away-goals rule after they drew 6-6 over two legs against Monaco.
Manuel Pellegrini guided City to the semi-finals in 2015-16 – their best performance in the competition – but Guardiola said his players are still gathering the experience they need in order to conquer Europe.
When asked how his team compares to the last eight in the Champions League, which includes Real Madrid, Bayern Munich, Juventus and Barcelona, he said: "We are far away. Not in terms of quality; in terms of how they played, that is the big difference.
"We lived in that in the Monaco game. We cannot forget how good they are, after what they did in Dortmund [a 3-2 win in the quarter-final first leg].
"We were able to score six goals in two games and we were out and that means it's how you live the whole situation, the 180 minutes and everything that happens.
"For that you need experience and hopefully we got that experience and it will help us for next season."