Here on the island we have some birds that look just like this. We call them Vini's. They are small birds and I do think yours is full grown by the look of it. I am thinking it is a bird like we have here. They come in flocks around our yard and we put out seeds for them to eat. They are adorable little birds and we love to feed them. When one comes to eat we normally have around 50+ show up all the time.
Looks like a Sparrow to me, 10 to 20 days old, here's some info on this bird- animals.mom.me/
Even if you are not an avid bird watcher it is fun to identify these garden visitors. Noting size & shape, color pattern, behavior, and habitat can help. There are books for your region and apps for your phone available to assist.