Why not make sourdough bread from young starter?
The advice to let the culture mature before you use it is targeted to getting reliable results. A mature sourdough culture has a relatively small number of strains of microorganism, which have outcompeted the others and formed a relatively stable ecology (assuming a regular feeding schedule). At that point the culture is reliable because newly introduced strains can't compete with the established ones. A new sourdough culture may work fine (particularly if you're seeing vigorous activity), or it may be not great, or it may be the best sourdough you've ever tasted. But the bread you make with it today may be significantly different from next week's.
As an example, if you got a bit of commercial bread yeast in there, the bread yeast is going to go crazy. But that yeast strain doesn't do well with low pH, so once the lactobacillus gains a toehold it'll slow down and be replaced by a hardier strain of saccharomyces. Fine bread this week; fine bread next week; but two different breads.
Bottom line: if you like the look of it, no reason not to use it today. Just don't generalize from the results.