I would be very comfortable suggesting this is A. aculeatus. Please consider adding at least one place where it can fully hide. Without a safe hiding place, it will be stressed and be less active. A full tank of rockwork is recommended.
A note of caution. I believe this one is full grown, typical of many octos from Indonesia. Since octopuses have a very short lifespan (between 1 year and 18 mo for most warm water species that we keep as hobbyists), be prepared for a wonderful but short time with your new ward. Here is a link to a thread containing a collection of posts that I recommend all new octo keepers read.
That is ALWAYS the question that is hard to answer and there are no guarantees no matter where you get the animal. It is also very hard to tell the age of all wild caught octopuses because they vary dramatically in size and health. I hold my breath for the first full two weeks to see if they fully survive shipping and transition into a tank. After that, age plays a major role. If the animal is very young or very old, it often does not make the 2 week full acclimation time. In spite of the downsides, however, I continue to keep them and enjoy their company.
I would be very comfortable suggesting this is A. aculeatus. Please consider adding at least one place where it can fully hide. Without a safe hiding place, it will be stressed and be less active. A full tank of rockwork is recommended.
The coloration, eye horns, eye star, arm to mantle ratio in combination (ie each separately are not specific indicators) are all consistent with aculeatus. Here are more images by @Neogonodactylus from our gallery.
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