Ming from Agents of Speech explains why developmental milestone charts don't fit every child. Instead of comparing to timelines, look at what your kid can actually do: join kindergarten, talk to other kids, speak clearly. If something's off, get a speech therapist to figure out what helps.
You need to understand that those milestones online may not apply to your child 100%. When you think that your child has a delay or disorder, you need to think about it from a functional perspective. So for instance, if your child is required to go to kindergarten by law, right, then obviously you need to look at if your child can function within the classroom or not. You don't need an assessment to tell you these things because you can see it already. If you see that your child has problems with playing with other children, speaking properly, speech intelligibility, meaning how much you can understand your child's speech, is low, by all means, you have to do something about it. And usually it starts off with an assessment. An assessment is always better because a speech therapist or a language therapist or whatever therapist there are, they are a lot more understanding. The difference between you and a professional is that professionals can see through, can read, at the very least can siphon through and think about what resources will apply to your child, which approaches apply to your child.
