Limping through Spanish acquisition

This morning, I was thinking about how I can't ever tell how old people are in person, but I REALLY can't tell when I just hear a voice, like on the radio.

I had the thought, "When I'm talking to you on the phone, I have no idea how old you are." As per usual, I wondered if I could say that in Spanish. So I thought, "Cuando estoy hablando contigo por teléfono, no tengo ni idea cuantos años tienes." 

When I put that into Google translate, it gave me in English exactly what I was trying to say! Yay!

But then I reversed them, because I do like to see what it recommends, this always makes me see that I have a way to go. 

What Google translate recommended was, "Cuando hablo contigo por teléfono, no tengo ni idea de qué edad tienes."

It's just a little different, but probably more polished. Still, it makes me hopeful that when we travel to Mexico in spring, I'll be able to make my way a bit better than if I were going in unprepared at all.