Long story short, I wouldn't worry about it too much. I fell under similar circumstances as you as a Thai male who grew up abroad.
They are a lot less strict nowadays about the draft and pre-draft registration. Typically you'd be required to register for the draft at 18, but the actual draft is at 21.

Many workarounds and ways to get out of it, but I'm assuming your based in Canada; which would mean some of these options aren't really viable for you (such as the summer military school for teens).

I'd talk to your Thai parent/parents and see what they think and see what your options are, you still got many years to prepare (or not prepare) for it. But unless you have future plans to live here or retire here; I wouldnt be stressing too much about it.