Most readers will imagine a younger male (which is correct), but the details aren't revealed until he looks at himself in a mirror, so the reader makes the discovery at the same time he does:

Staring back was a young man, about twenty-five, black hair cut short on the sides and squared flat on the top. He recalled this was the standard style for first year students, so all cadets were required to copy. After that, more personal leeway was allowed in the regulations. He took his fingers and rubbed the light brown skin of his chin but felt no evidence of growth or stubble.
Tammon tried to examine the figure looking back as nonchalantly as possible. Skin richly tanned, and he recalled that was slightly darker than the natural color. He had an average physique, the muscles in his chest and arms pressing against the fabric of the uniform. His eyes were a very dark brown, dark enough that it blended in seamlessly with the pupil. Other than that, there was nothing else warranting closer study.

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Hopefully, this creates a memorable "Ah-ha" moment to be shared between the character and the reader.

I lay there in the dark talking to her. I asked her questions. Where are you from? Why did you come here? What happened? What was your life like? How old are you? I got no response, of course. Wasn’t sure she was still alive.
I told her my entire life story. I confessed many things that I’d never revealed to anyone else. Including myself.
How I was strong and self-assured on the outside, but inside? Not so much. How I’d come to the road less traveled, but had stayed on the freeway.
How I had dumped the only guy I’d ever truly loved because of my stupid music career, and all my tours. How I often studied myself in the mirror, standing sideways, wondering if I should bother trying to keep myself slim and in shape, or whether I should let it all go and enjoy my cheeseburgers. How I knew I could never go for Clay, even though I knew he had a big crush on me, and he’d be a damn good catch for an aging chick like me.
How I’d never even tried to publish the songs that were the most important to me because I didn’t think they were marketable, and instead churned out all these maudlin ballads. Which of course made me a shitload of money, and allowed me to buy my dream property here on the coast, psychically as far as possible from La La Land. But which left me with this empty hole here near the core of my being.
I began to hum this one melody I’d written years before, and had never performed in public. It was my internal anthem—the music for my secret self.
My alien companion, lying in the dark covered by a horse blanket, in a tiny, squeaky voice, hummed along with me.

I can see them perfectly! 😊😊😊 Great job.

You are welcome!

Here's a description from my WIP; would love your feedback! Set-up: Caro and her best friend Patty are grocery shopping; a man they don't know has just stopped to look at them.

They make an odd pair, Caro and Patty—like a wizard and a pixie. Patty is petite, with sparkly eyes and a sweet, impish smile that reminds Caro of Meg Ryan’s before the plastic surgery. Wispy, silvery-white wings of hair sprout from her head like dandelion fluff. Caro—long-faced and five-foot-ten—feels like a lurching, dour beast in comparison, despite her still-slender figure and still-ginger hair. That hair is cut in the same relatively expensive, relatively stylish, shoulder-length coif she’s sported for more than twenty years, because why mess with success and introduce another variable to be monitored and adjusted into a life full of more important things to monitor and adjust?

You are welcome!

Thank you!