Neutering may calm him if he hasn't been done but he sounds quite normal. My seven month old female kitten behaves the same way - leaping from the top of one thing to another - backs of sofas, windowsills, chests of drawers etc. It's worse than having a two year old in the house . If I take her out on her harness she just sits and looks at me or chews the grass, though she has started to want to explore a little more over the past few days.
I won't be letting Mai Tai out on her own but you could try taking your cat on a harness to get him used to the idea of outside before giving him his freedom out there. If he's not neutered yet though I'd get him done before you let him out on his own.
All the best x

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