I started when I was in my 20s. My husband and I had moved to a home that already has a beautifully manicured lawn and gardens that were overgrown. My brother was an avid gardener, so he came over and helped with the weeding, which was much fun, but he also encouraged me to go to the nursery. We spend probably 2 hours there, looking at all the wonderful plants. He explained to me the difference between annuals, perennials and biennials.
Over the years, he taught me to look at growing conditions, like sun, shade and water. To always look at how big the plant got, and what kind of habits it had, was it trailing, did it climb, was it something that needed to be staked, etc. He also showed me how to look at not just the blossom, but also at the leaf structure and color - so you could have an interesting garden even when the flowers weren't blooming. He taught me so much. He died when I was in my 30s, but I still think of him every time I'm in the garden.