There are a number of ways to tell young hummingbirds apart from the adults. While their appearance can be similar with some subtle differences, their feeding habits can be a bit more obvious. Adult birds always revert back to the easiest sources of food that require the least amount of effort. They learn over time that expending more energy to gain the food is counter productive. This is precisely the reason feeders become popular with the adults. Food is survival, and if more energy is used in gaining food than what the bird gains from that flower, it simply gets rejected over time because their lives depend on it. There are certain criteria that make a food source worth while. Color is an initial attractor, but it certainly isn't a requirement in making a flower great. It's all about the food within, and the ease of obtaining it. A flower may have the sweetest nectar and an abundance of it, but if it's difficult to access, adult birds may find an alternative. The opposite can be said for young birds. With the slightest taste of sweetness, they will go all in and dig for their lives. You can often times hear young hummingbirds slapping around in the petals of flowers, but the adults remain more graceful and choose the easier foods.
This young Ruby-throat was getting a grip on the petals while digging deep for the sweet nectar in this Vining Nasturtium.
N.E. of Edmonton, Alberta, Canada. August 24, 2017.