Other question, why you use ablative form for "firesof" and not genitive form ?
Sigh. Because I'm dumb. It's not that it couldn't work. Since I was trying to create a hypothetical slightly contracted experssion, there is a lot of leeway. But this particular attempt messes with the way zero copula sentences express time, so as guesses go, it's unnecessarily messy.
You see, I wanted something less contracted than "I'm 35" and more contracted than "I'm 35 years old/of age". Going simply with "I'm 35 years" (Anha chisen ma mek firesof) felt like a lazy attempt. I'm not really a bunch of years. I'm a human and a wee bit fat, but the years are what I've been through, not what I am. I figured Dothraki would probably do a little better and use a preposition or non-nominative case. I might have gone with a preposition like
vi or
ha, but since prepositions are sorta like extensions of the small case system, you should usually go with bare cases unless they feel insufficient. The core sense of ablative case is
origin or
source, ie. "from". That was a tight fit, so I went with it; a very reasonable guess at face value.
Had I taken a second look, I might have noticed that a zero copula sentence (which this is) has a well established special sense on putting the second word (I think that's
predicate in the linguistic lingo) in ablative, it's how a zero-copula sentence is put in the past tense. So, frankly, I more likely managed to say "I was 35" than "I am 35".
Further note: this has nothing to do with the number thingie. AFAIK, in nominative "35 years" is
chisen ma mek firesof (and 24 years
chakat ma tor firesof), and as with any noun phrase, you need to put it into a correct case if you want to use it in a sentence. The number part does not inflect and does not affect how the noun inflects (though interestingly for animate nouns the noun can be in plural but does not have to be).
I'm afraid that this might be one of those explanations that confuse more than actually explain, sorry. I tend to overthink and that tends to show