It's You vs You. No one else.

I have lots that I could say, but this'll be quick. Stop comparing yourself to other people.

Yes yes, it's fun to see how you stack up against others. But I absolutely do not like congratulating someone for something only to have them say, "yeah, but so-and-so did such-and-such." Well you know what? I don't care. I don't care one stinkin bit. 

Every single person on this planet is different. We all have certain advantages and disadvantages prewired within us that we owe to our unique characteristics, dimensions, and proportions, and comparing oneself to another continuously-changing individual makes even less sense than measuring a growing child's height by standing them next to another, also-growing child. In order to see change, you need a standard, a constant; something by which to accurately asses progress or quantify change. We measure a kid's height on a door because the door isn't growing, and thus will truthfully represent the changes taking place. The truth there seems obvious in this particular setting, but not so obvious in a fitness domain.

If you want to see whether or not you're progressing, don't compare yourself to other people; compare yourself to your yesterday's self or last-time's self. If you've improved, you've improved, and you should be psyched about that. Just because you, the 43-year-old, aren't making gains as quickly as her, the 19-year-old, on back squat doesn't mean a single thing at all. And just because you, the 27-year-old, aren't making gains as quickly as him, the other 27-year-old, doesn't mean a single thing at all either. The differences between these individuals are so incredibly great and are so much more complex than their age that a comparison between the pairs would be downright silly.

[I would like to pause here to make my disclaimer: if you are a competitive athlete, you have to compare yourself; that's the way competition works. Otherwise it wouldn't be a competition. Thank you.]

Long story short, comparison kills. Be proud of the progress you are making, and don't worry about where anyone else is. If you give your best every day at every opportunity, you're right where you need to be.