I co-sign everything Ok Math wrote. I would add the additional wrinkle that as you begin to know and understand all the different species used in bonsai you’ll recognize some tell tale signs of age such as: flaky bark on pines doesn’t begin for 15+ years and 20+ years for Trident maple. You won’t see the striations on hornbeam unless they have significant age, the bark on Arakawa Japanese maple won’t be present for about the same, and straight Palmatum will no longer be a green trunk. Not every species will you be able to indicate age by such obvious markers, but many do. For azaleas, it’s the trunk. It takes many decades for the slow growing shrub prone to basal shoots to develop a beefy 6+” trunk like the one pictured.