How should I relate to milestone charts? Is it a problem if my child isn't on schedule by age?

Milestones are a guide to "the age by which most children (about 75%) become able to do something," not a pass/fail line. What matters is not the age of a single achievement but "whether the child keeps progressing in their own way." Even if they're behind the chart, it's often fine as long as they're moving forward; if worry persists, don't just wait and see—consult at a checkup or with a pediatrician.