18andfree:
My goal is immobility in the next four years
Be as lazy as possible. If money is not a concern, order every meal in and only get up to use the bathroom or to get more to eat. Ideally, getting a step tracker and setting how low you can get the number would be best.
Drink "dirty soda," some sort of soda with cream or half and half, syrups, etc. It can take a 500cal gas station drink up to over 850 in the same volume. Drink as many calories as you can.
The more you lay around and do nothing, the more your muscles will atrophy. You might not gain a whole lot for a while despite everything because you're losing muscle mass as you're gaining fat mass. And the faster you grow while your muscles get weaker, the closer immobility could be. You might have issues with your gallbladder which can slow or reverse progress, so jump on those early so you can keep growing. Don't get discouraged!