Yeah the 50 years old thing doesn’t really make sense. I get the ‘some species age differently’ thing, but if that baby is 50 then 900 would be a pretty young age for Yoda to die at.
My wife had the same complaint. But I pointed out to her that perhaps not all species age in the same proportions. For example, a mouse* might spend a smaller percentage of its existence as a juvenile than a human does. This is largely because humans have larger, more complex brains that take much more development and thus we spend a larger percentage of our lifespan as children. Perhaps Yodas have even more complex brains and take even longer to mature?
*according to Wikipedia the upper limit of a common mouse lifespan is about 3 years. They mature into adults in about 6 weeks, thus spending about 4% of their life as a juvenile. Using Wikipedia data of a current normal maximum of 104 year for human lifespan and a maturity of 21 (the Internet gives a range of 18-25) humans spend about 20% of their lives as juveniles).