These are those points in development when you are "supposed" to achieve something, whether it is walking, talking, feeding yourself, being potty trained, cleaning up after yourself. Some of us never achieve the latter.
These are things that parents, doctors, specialists focus on when they are talking to a family with a child with Down syndrome, in that they usually say something to the effect of "don't expect your child to reach these milestones on time." On time. What does that even mean? As a "typical" child I refused to learn how to read; I loved having my parents read to me and so didn't see the point in making myself do that. Now I can't stop.
It took my brother about a year long to begin walking and now he plays football, tennis, soccer and volleyball. He will go outside and play basketball in the driveway by himself. Sometimes it's hard to get him to come inside.
I can't remember at what age he started talking, but for the longest time I was the only one who could understand him. He used sign language for a little while, which is a fairly common practice with any family with a child with any disability. He still uses signs sometimes. But, most of the time, he does not.stop.talking. You get him in the car and it is just constant chatter.
So, my point is, yes, there are goals to work towards. But no one should ever be discouraged from meeting any of those goals, "typically" developing or not. Doctors should never tell a family "Don't expect to understand her verbally" "Don't expect him to be able to live by himself." That is discouraging. That is why parents worry their hair out about their child not walking when their other child started or not being able to tie their shoes at age 10. It might be difficult, you will probably need some help, but everyone EVERYONE is different. Things happen when they happen and if they don't, they don't.
"Gond, grant me the serenity to accept the things I cannot change.
The courage to change the things I can.
And the wisdom to know the difference."