Agree with the above. If at 16 he is anyway anxious about getting to the railway station "in a foreign country" then, as suggested, getting the Alsa bus from T4 at Madrid airport would be easier. You do need to book in advance, but this is easy. I always find
www.movelia.es/en easier to use and navigate and pay, than the
www.alsa.es/en site, even when booking an alsa bus. The bus service is excellent, if not superfast. But beautiful, clean, comfortable, well-featured: headphones, sweets and bottle of water supplied IIRC, and this was the regular, not the luxury service. When I was getting it last year, to Logrono, even with pre-printed ticket, he insisted on passport identification against his manifest, and didn't bother with the ticket. I guess this was because the bus was going to be full.
I will be getting it again to Leon 3 weeks yesterday!!
Enjoy your time together!