The neighborhood where your character grew up can change a lot over the years. This includes both the natural aging of the buildings and environment as well as your character's memories of that neighborhood. And just like that neighborhood, your character will change within that neighborhood as well.
If your character was raised within a city or large town, try to focus on just their local neighborhood. Try to keep your efforts to ten buildings or less. Was the neighborhood filled with just families and their homes? Or were there any businesses (e.g., markets, schools, taverns, etc.) within that neighborhood? Were your character's neighbors all very friendly, or did they have to constantly hide from neighborhood bullies or thugs? Was it a filth-ridden neighborhood, or were the streets paved with gold (literally or figuratively speaking)? Most big cities and large towns have a good mix of these extremes and everything in between those extremes. Feel free to get creative with your descriptions of the buildings and the people. If this helps, work with your DM/GM who may already have an idea about what the town or city looks like and they may be able to help you narrow down what your neighborhood looks like, too.
If your character grew up out in nature (e.g., forest, cave, field, mountain, tropical island, frozen wasteland, desert, etc.), try to focus on just the buildings and people within your small village or encampment. Don't go further that about 100 feet (30.48 meters) outside of the village or encampment. When trying to describe a small village, picture in your mind the example of a "Wild West" town from the movies or TV where you have a single street and all of the buildings stretch along that one short street. For your village, describe what buildings/businesses line this singular street. What kinds of people populate this neighborhood? Was your village filled with farmers, or was the entire community part of the Cult of Cthulhu?
For an encampment, describe the types of shelters (e.g., tents, yurts, tipi/lodge, etc.) that have been constructed which might possibly be able to be broken down and transported as needed. Is this a tribe of druidic nomads, or is it a war party traveling to or from a battle encounter? Were there any other children in the encampment, or was your character a slave or servant to a traveling noble? Is there a specific area that your encampment stays within, or are there numerous locations where your group has set up camp? If this is a traveling group, what is the reason for the semi-frequent travel (consider the Romani of Eastern Europe or the Vistani from the D&D adventure The Curse of Strahd).
If your character grew up within a cave system (dwarves are popular for living in this type of environment), how were the caves and tunnels created? Were they cut through over thousands of years by an underground river system? Or were they carefully crafted and sculpted by the purposeful chink-chink of picks and axes? Were there any creatures, predators, or enemies that also lived within this cave system? What was your character's typical source of food and water?
If your character grew up in a ground-based technological society, what kind of technologies were commonplace in your neighborhood? Was this a seemingly utopian society such as those found in science fiction movies and books? Or was this more of a dystopian warzone such as those commonly found in Warhammer 40,000 games? Is your society entirely human or human-like (androids) like in the book/movie Blade Runner, or are there various types of alien species as well like what is found on most Star Wars planets?
If your character grew up on a space cruiser, did your ship ever stop at and travel down to planets along the route? Did they spend their entire life (birth to present) aboard this ship, or did they come aboard at some point during their childhood? What did your character do for fun aboard this ship? Was it a military or civilian ship? Did your character have any duties aboard the ship while they were growing up?
As you can see, every neighborhood environment can be very unique, especially to your character. Feel free to get as creative as you want in describing the neighborhood and the people that populate it. If there are any memorable people within the neighborhood, don't forget to describe them and give them a name as well. For example: "I remember ol' Mrs. Radagast at the corner market and her scaly red tail because she always gave me a small piece of candy when I came into the market with my mother."