Sandbox mode?

I'm starting to play AoE: DE and I absolutely love it.

I put it on Easy for a Custom game and really, I just wanted to mess around and build a cute city and an impressive big army, which I remember I use to love doing back in the day.

Although even on Easy, the AI is pretty insanely aggressive. They're pouring out Elephants at me keeping me on my toes and working my army down, I eventually win without difficulty but kinda defeats what I wanted to do. I think I recall back then there was an "easiest" mode that let me do that. Any ideas?