How old is Thoris? Like when you say he's not actually that old, what do you mean? For Vulcans, 70 is not that old but I would say it is.
Nope! Nuh-uh! Not gonna! I'm gonna answer anyway! (<3)
Now, I shan't be giving out an exact number for Thoris' age, I will tell you a bit about the Andorian lifespan in Emigre's era and give you some context.
Andorians and Humans actually have very similar lifespans canonically, with a max age of about 130-150 years in the later eras. Since Emigre takes place fairly early in the Trek timeline, however, human lifespans aren't quite so long and I think, given the medical innovations of the day and age, neither are Andorians.
So, for the time that Emigre takes place in, let's say the average life expectancy of Humans - assuming no major injuries or illnesses are involved - is about 100-120 years old with the advances in interspecies medicine, reduced pollution and nanoplastics/general environmental poisoning, and overall quality of life improvements. This is in huge part thanks to Vulcans, whose technological advances allowed Humans to clean up their energy and food productions practices immensely, and whose medical technologies allowed for not only better treatments in general but earlier detection for disease, gene-tailored medication, and generally higher success rates for complex treatments and surgeries. The Interspecies Medical Exchange improved things even further, of course.
All of that being said, Humans are still only about 200 years removed from multiple major nuclear events which would have lasting effects not only on the planet but on the surviving populations themselves. All the medical intervention in the world can't completely fix what massive, long-term radiation exposure does to a person's genetic material, even in the Trek universe. So, regrettably Human lifespans are still hampered somewhat at this stage in the timeline.
Andorians, meanwhile, are holding steady at their 130-150 year lifespan and have done for centuries now. While they physically mature in roughly the same timeframe as Humans do, they live significantly longer, so an Andorian's idea of 'middle age' isn't quite the same as a Human's.
We would be inclined to say that the 30s-60s are the middle age decades, because Humans like to divvy our lifespans up into neat sections, where 0-29 is youth, 30-59 is middle-aged, and and 60+ is advanced. Definitions shift over time, of course, but for the sake of simplicity, we're going to stick with the older, slightly outmoded generalizations (which I personally suspect this is a holdover largely in part to the shorter lifespans Humans had historically, where reaching anything above 60 was a very impressive feat indeed.)
Conversely, the 'middle' of the Andorian lifespan is generally considered to begin in their 60s, with advanced age beginning after their 90s. This effectively leaves you with a culture that has a prolonged youth and shortened middle ages and relatively brief advanced ages.
So, when I say that Thoris is considered middle-aged, roughly mid-middle aged even, you now have a little more context for what that actually means.
<3
(Forgive any misspellings, grammatical weirdness, etc - I'm in the thrall of a week-long tension headache.)