Back in the day ago<good?> old days, when I was a child, I spendedt a lot of time with my older brother and cousin.

Less professional and more slangy = "back in the day"

All the time wWe played outside, all the time and created our own games.

For example, we had a game with rules where one had to destraoy an oppeonent's ball by throwing off yoursyour ball from some certain height.

I don't really understand how to play this game :). You throw YOUR ball and it destroys the opposition's ball? How?

Positive memories. Part 1.

This is correct, but we would often use the expression "Happy memories" instead.

Back in the day ago, when I was a child, I spendedt a lot of time with my old brother and my cousin.

All the time we played outside, createding/inventing our own games.

We would normally inverse the text to say "We played outside all the time"

For example, we had a game with rules to destraoy an oppeonent's ball by throwing off yours off from somea certain height.

We lit fires and ran around the backyard.

Again, this is correct, but we would more easily stay "We started fires..."