Just don't call them "years", call them an "orbit". Presume they are past their local Copernicus; they know their world orbits a sun (or planet).
"I am three orbits old; that means I am officially an adult and no longer my parent's responsibility, I can vote, I can get married, I can drive on my own, I can go to college."
Of course you should do that in a scene. But just get used to making it a part of the language, they measure long time in "orbits", and perhaps shorter time in Seasons (if the orbit is not circular, like ours is not circular) or "quarters", a quarter of an orbit, or "quints", a fifth of an orbit.
Do not try to "borrow" English terms for their measurement of time, or distance. Even on Earth, not everybody always used the same terminology for these. Such measures are idiosyncratic; our word "mile" comes from the Roman "milia passum" which was "one thousand paces", each pace was five "feet", but the measure of a "foot" was different for Romans, so their 5000 feet was our 5280 feet.
All of this would have no meaning to aliens, they will have their own idiosyncratic measures for distance, weight and liquids, and they will have their own idiosyncratic measures for time as well.
Your story will not seem realistic if you just borrow English words for all of this. Make up your own history of how their measurement system originated, and use your own words.
Readers will get used to them. Due to tracking child development, if it occurs roughly on the same schedule as humans, you are going to need subdivisions of the "orbit". You cannot put first graders and sixth graders in the same classroom, they are going to need subdivisions of the orbit that approximate an Earth year, and probably Earth Seasons within that. Perhaps weeks as well (and "7 days" is also an entirely arbitrary number of days in a week, roughly based on quarter Moon phases, which aliens might not have.)
Edit: Jack Aidley in the comments claims "Invented units are a bad idea. "It was four k'aih to their camp" communicates nothing and a text with many invented words rapidly becomes irritating to the reader.
There is an element of truth in this. First, do not make your invented units difficult for a reader to pronounce and remember. Second, always invent a way to introduce your measurement systems in context, and in isolation, meaning don't use your time measure to explain your distance measure, like "a kilometer is a 12 minute walk," or "a mile is a 20 minute walk," unless the reader has a good grasp on your time measure.
Keep in mind the real-life disparity between "Fahrenheit" and "Centigrade", or "Kilometers" and "Miles", "meters" and "yards", "liters and gallons", "kilograms and pounds".
To an extent, this is all about context. In centigrade, 10C is chilly, you need a coat or at least a sweater (50F).
As a writer, ultimately, the measures only matter in how they affect your characters, physically or time-wise, and that is how you introduce them. What does a baby weigh? How far is it to school, and how much time does it take to walk there? How long is it between meals? How long do you normally sleep? Implicitly explain your measures by "show, don't tell." Use them in relatable circumstances within scenes.