As someone who has spent a great deal of time thinking about this very thing, If you are serious about starting to gain on purpose in the future but not yet, here are some things you can do:
1. start stretching your stomach now with low calorie foods
2. start budgeting for food now and learn to cook if you can't already.
2. begin a workout program that you can continue to do while you gain.
3. Start mentioning your desire to gain weight to people. It will be less of a shock to people when it does happen, and maybe you will find some people in your corner who want to help you on your journey.
4. Find mentors and colleagues. Establish relationships with people that are already fat and happy, people that eat the way you will want to eat when you are gaining, people that treat fat people with love and respect, and learn from them.
5. Stabilize your life, Don't wait until you start gaining to go to the doctor on a regular basis. Get established at your job. Nail down your living situation. All of these things have derailed other people's journeys before they could get off the ground,
6. Start figuring out what you like, what you don't like, what you can do everyday, what you have to save for special occasions, how you want to track, when you might actually go for it, Establish your goals with timelines and milestones.
Good luck.
3 years