Yes. Speaking from experience, I put on 30-40 lbs of muscle in about 6-8 months without any professional help/guidance. My routine was a breakfast drink, protein snacks, double order of Steak & Shake for lunch, protein snacks, workout after work, protein shake, two Chipotle bowls for dinner, protein snacks, then a mass gainer before bed. Rinse, repeat. Any type of professional guidance would've helped make this cleaner/healthier/easier, but it's extremely possible to add weight through muscle quickly.
He won't have any problems adding 20+ lbs if he's serious about it.