Between 12 and 15 months
There are large individual differences, but the norm is that children begin to walk when they are between 9 and 18 months.
Most people take their first steps sometime between 12 and 15 months.
Nobody has a clear answer on exactly what is needed for the baby takes its first steps.
Strength and control
Babies should have the strength, control and stability in the hips. In addition, they must have control of the neck to adjust the balance. They must also have established coordination with every arm and leg. This is the same movement patterns they learn when the crabs or eels forward on the floor.
First, children go with arms up to get better balance. They go in standing position, using all forces and all concentration to go. Eventually, they put the arms down. When they discover that they can bring toys from place to place, and they could not do it when they were crawling. To beginners toes are often pointing in many strange directions, but straightens out when they get better control of time.
Personality and temperament also had an impact in addition to have the fine motor skills.
Children have a different point at which they release themselves. It is perhaps the best that the motor learning is individual. Some throw themselves into new challenges, some are practicing a lot and others will be sure that they master something before they try something new.
Older siblings can be a great motivator.
But that does not mean that the siblings begin to go at the same time.
Motor is in the genes, and you can see that the siblings in some cases have the same motor development. But there are also some examples of the opposite.
The baby’s size is not of great importance. Large babies with proper temperament and motivation may go earlier than light babies.