I believe spirit guides can be noticed/met once you are spiritually in tuned with yourself. Mediation of course is the first step. It may seem hard at first, but you just need to relax, and find a comfortable position. It is through meditation that you may have an encounter with your spirit guide.
Meditate and when you are ready call for your spirit animal to reveal themselves. That's how I discovered mine, a white shark ^^ check out other spiritual forums too they have loads of information on contacting and discovering your spirit animal.
I remember reading a method somewhere where you relax and imagine yourself in a place in nature, like a beach or a forest, and ask your spirit animal to come to you. If you wait a little while, the spirit animal should appear. I've never tried this, though, but I would be interested to hear if it worked or not. Another way to find your spirit animal is to take a shamanic journey with the intention of meeting your spirit animal. This is the way I did it.
I met my spirit animal when I was around three years old. I'm curious as to how and why this happened and if it means something. Has this happened to anyone else - meeting your spiritual animal at such an early age? Also - I haven't been in contact with him since - could I have permanently lost him? I feel that my questions might be a bit stupid and if that's so - I'm sorry.
From what I've read, spirit animals are there to help you, and they will leave if you don't need their help anymore, but a new spirit animal will come. You will always have one. You should try contacting your spirit animal again, and it may not be the same one, but that would be a good thing because it would mean you learned what you needed from it :)
I don't know anyone else who met their spirit animal when they were so young, so I don't really know much as to why it came to you at such an early age. I can only guess that maybe its because you were really in tune with the spirit world when you were younger or maybe you just remember it when other people might not.