Is the American Robin discriminating based on age?
Apparently for the American Robin, age might be a sign of plumage (oversimplified: how feathers look), and the American Robin could make mating decisions based on plumage. It's highly speculative to claim that the American Robin selects their mate based on age, but there's credible evidence that they may make their selection based on plumage Source below.
Perhaps the American Robin does not engage in age'ism, but looksmaxxing seems like a worthy move for a single bird.
"The pattern of assortative mating by plumage traits we found could also arise if mate choice (mutual or by one sex only) is based on a correlated trait that co-varies with plumage, such as age. Numerous studies have suggested that expression of melanin-based ornaments can be age-dependent (Manning 1985, Andersson 1994, Sundberg and Larsson 1994, Gil et al. 2001), and assortative mating based on age is well documented (e.g., Sundberg and Larsson 1994, Komdeur et al. 2005). There is no way to age American Robins in the field, and because we examined this population for only two years, we had little information on the birds' age. That information did not indicate that plumage varied systematically with age, but a much more robust analysis is needed before a conclusion is warranted."
source: https://academic.oup.com/condor/article/113/4/881/5153070?searchresult=1