Just Eat potatoes without any second thought, open the 'Google' and write 'potato nutrition facts' and see Potatoes are rich in Vitamin C, Potassium, Carbs, Vitamin B6. In short its a good combination of natural minerals.
Boiled potatoes are hard to eat, instead bake them, and eat before 2-2.5 hours of workout. Start from 1-2 medium size and increase gradually. Don't eat too much.
Its from my personnel experience, potatoes are very very good. Bro, you are just 19, EAT EVERYTHING.