According to some research, babies have to form the attachment with their caregiver during a Critical period.
This is between birth and 2½ years old. Bowlby said that if this didn’t happen, the child would be damaged for life – socially, emotionally, intellectually, and physically.
Bowlby viewed this more as a sensitive period.
If an attachment is not formed at this time (2 years old), a child will find it much harder to form one later.