Noob help! Mixing soldiers and economy for aging up.

As the title says, I am a noob when it come to playing multiplayer AoEIII. I can do fairly well against the AI but when I play against other players I can't seem to mix building soldiers and my economy so I can age up. I always get crushed in the 2nd age because I don't have enough soldiers. but then when I do build soldiers I don't age up to level III as quickly as my opponent. I mostly am playing as the dutch and Germans. Which is weird cause from the videos I have watched they have a very strong economy. I just can't seem to replicate it when I play online.