Can a skinny person get a fat? How?
Getting fat and gaining weight are two things. Every person has a 'saturation point', an upper bound of weight after which there is no more weight gain, and a lower bound below which you cannot lose weight. If you are looking to add a few extra pounds, make sure you do it healthily.
But if you are asking for a recipe of disaster, I can tell you, because I gained 72kg in the past 6–7 years! And I am only 24 years old!
A skinny person can get fat with age, firstly. Even if your diet does not change, the effects are seen a year or two down the line. For me, my weight gain owed to eating large portions of food, even if it was home cooked. Add a load of sugars and soft drinks on that (6–8 glasses of Coke a day!), and also junk food, our mortal enemy. I used to weigh 80kg back in 2010, and weighed 152kg in June 2018. Thankfully, I have repented from my ways, and have managed to lose 30kg in 2 months. It's time to go back to 80kg.