You're not behind. The anxiety from watching others' milestones on social media comes from a race that doesn't exist. Each person's journey is different, so stop comparing yours to theirs and move at your own pace.
Chapters
It can be overwhelming to hop on social media and to see all of the different stages people are at in their lives, but what you have to understand is that there is no race that you are running on. You are not falling behind in life. Understand that because you choose to consume in a manner of comparison towards others, that's exactly what you're going to perceive the situation as, as a race. But in reality there is no race. You're on your journey and whoever you're looking at is on their journey. So once you realize that there is no race, there's just so much peace in going after whatever it is that you're going after because there's no need to compare. You just go.