He can't speak and makes baby noises. His being 50 is irrelevant; he is at best a young child. Like, toddler to preschool age, and often coded as even younger.
(That's one of the criticisms I've seen of the movie; it's very inconsistent about exactly how mature Grogu is. )
But my point is that I don't buy the idea that it's just proportional to his species's lifespan. If he's conscious and capable of learning at all, then there's no way he could have 50 years of life experience and not have gained anything from it. Someone who's lived through 50 years' worth of events, no matter how childlike they are in physiology, is going to have a hell of a lot more actual
experience than a 30-year-old human, say. I mean, isn't that the whole point of Yoda being 8-900 years old, that he's got more than 10 times as much accumulated life experience and wisdom as a human? If his species somehow learns at 1/10 the rate, then what's the point of even giving them a long lifespan if it's just going to cancel out?
(I have the same problem with "Miri" in
Star Trek. Okay, so these kids' physical aging has been slowed by the mutant virus, but they're still 300 years old and should therefore have gained a hell of a lot of maturity through accumulated experience, so it makes no sense for them to still be acting like preteens. Sure, the brain doesn't fully mature until the 20s, but life experience matters. I've known teenagers in my time who were more mature than a lot of adults.)
Granted, there is
scientific research suggesting that both maturation rate and longevity are proportional to the complexity of the brain, because it takes longer to grow a more complex brain to maturity, and because a brain with more cortical neurons can remain viable longer as they gradually wear out. So maybe the idea is that Yoda-oids (Whills?) mature more slowly because they have much more complex brains. But I think Ahsoka told Din, as
Xerxes82 mentioned, that Grogu's development is actually arrested for his physiological age because of his psychological trauma during the Jedi purge.
Yoda lived until 900 y/o.
So 50/900 ≈ 5.55…% of their life span.
Assuming a average Male Human Life-Span of 80 y/o & similiar linear aging to our human species, 5.55…% would be the equivalent of a 4.44… y/o Human child.
Not necessarily. In different species, the various stages of life constitute different percentages of their lifespans. For instance, elephants gestate more than twice as long as humans and their “baby” stage (before being weaned) can last 5-10 years, far longer than ours, but they reach maturity around the same age as us, c. 18, and have about the same overall life expectancy, 60-80 years. Parrots reach sexual maturity in just 1-4 years but can live 80-90 years or more. So it’s pointless to even try to make analogies between species’ life cycles.
This is even more the case in fiction. Vulcans are known to live over 200 years, but Spock matured to adulthood at the same rate as a human. And since Spock and T'Pring are agemates, given that they were betrothed at 7, we know this applies to full Vulcans as well as half-Vulcans. Also, Alexander Rozhenko aged in soap-opera time and went from conception to adulthood in only 8 years, but Kor, Koloth, and Kang lived to between 100-150 if Odo's estimate was accurate.
After all, aging is not a monolithic process. Maturation and senescence are opposite processes -- in the former, cell growth dominates over cell decay, and in the latter, decay dominates over growth, with adulthood being the period in the middle where they're balanced. So it stands to reason that there'd be no direct correlation between the speed at which a species grows up and the speed at which it grows old.