It wasn’t obvious because of the age, it was obvious because people don’t say “back when I was in school” to refer to a doctorate. And when the context is specifically trying to emphasise how young they were at the time, they don’t tend to mean “when I was an undergrad”, either.
Hm…I’m seeing that millennials are between 29 and 44. Even 29 is old enough to earn a PhD.
Either way, the older ones are definitely old enough to be talking about post-secondary.
It wasn’t obvious because of the age, it was obvious because people don’t say “back when I was in school” to refer to a doctorate. And when the context is specifically trying to emphasise how young they were at the time, they don’t tend to mean “when I was an undergrad”, either.