What electric shaver would u recommend for a new shaver? It is only for his mustache area?
A blade. 
If he’s insistent on an electric shaver, he should take cues from his father/grandfather to determine how his beard will grow when he gets to that stage. Electric shavers are not cheap, so it really should be viewed with the long-term in mind. And so much of it is personal preference. I find the foil type like Braun results in a closer shave than a rotary type like Norelco, but they also tend to be more expensive.
When my S was that age we got him a lower end Braun. Costco sometimes has them on sale.
I got both of my kids a Panasonic for sensitive skin. They have lasted years, with replacement blades.