It sounds condescending and foolish to say explicitly like that, but not one intentionally lets themselves go to seed, it just kind of sneaks up on you while you're doing other things. Doesn't even necessarily involve age, just getting used to a more sedentary lifestyle and then finding it stuck - after foot surgery last June made me stay perched with my feet up perforce for a July and some of August to let it heal, and it just compounded until back during that January cold snap I could barely get up from a chair and the burns I went into the emergency room for ended up being a side issue to having put on so much weight in water that half my lung capacity had vanished along the way and the cardiologist was surprised I wasn't having constant chest pain from the amount of chest constriction.

Literally over sixty pounds worth peed off over about a month with the relevant medication, and still going down slowly, but the point is that it was never a choice to be a lump, just continuing to do the stationary things I'd always preferred but sometimes interrupted for other tasks until the habits changed.