If your goal is noticeable, bulging, muscles, you should push yourself with weights or doing body weight exercises. You will want a specific plan to meet your objectives. The plan probably involves a certain way of eating, and/or supplements, in addition to time in the gym.
If your goal is to increase health span (not just to live a long time, but to maintain mobility and strength as long as possible), your program will look different. Pushing yourself with weights is important (with the proper training and building up appropriately), but so too are exercises designed to maintain and even increase your mobility.
At the gym, remember your goals and stick to them. Let everyone else pursue their own goals, whatever they may be.