Depends on what “bigger side” means. People have this warped sense of what a body should look like, that if someone has a little bit more body fat but it’s really healthy and strong and can do simple tasks like walk upstairs without losing your breath, than being bigger doesn’t necessarily play a factor in their health, therefore telling them to go to the gym would be a dick move because it would be purely based on aesthetics and not actually about their health.
But if they’re obese or struggle with these tasks, eat super unhealthy, never have any exercise ever, than it would be beneficial to encourage going to the gym. Then again the gym in general is a good thing to add to someone’s life, but if you keep insisting it purely based on the fact that you want him to look more pleasing to you, it might be time to find someone else.