Yeah, spirit guides and guardian angels are largely the same things, just with different names and connotations, and they can indeed be animals that you’ve had throughout your life. My brother had a cat that meant a lot to him and after it died it started hanging around him. The problem is to tell apart whether the SG is actually that animal or your SG taking the form of that animal because that’s what you need at that point in time, not that it really matters which in the long run. For telling the two apart, I made a post on that a while back, which can be found here.