How do I tell if my Gas Bicycle needs an oil change?

Hi, I'm new here, but I joined here to learn more about this great hobby and maybe someday help other people

But anyways,

I have a Subaru 4-stroke engine mounted on my bike and it uses standard motor oil. I'm though, not sure how to tell if the engine needs an oil change. When I read the stick, it is brownish color, a little bit darker than honey.

I heard of a technique by putting a drop of oil on your finger and if it is too sticky, it must be changed? Is this true? Any help on this will be greatly appreciated

I have had about 125 miles on the bike in the first week I've had it

Please also let me know if this is the wrong section.

Thanks everyone with your prompt responses. I will go with the manual for now and change the oil every forty-fifty hours or so. If something goes wrong, I will let you guys know.

-Thanks!