多，means "more than" here. 两岁多。more than two years old. 378来多长。 56块多。more than 56 yuan 10个多月。more than 10 months 20多岁。more than 20 years old 580多人。more than 580 persons. 400多块钱 more than 400 yuan

两岁，2 years old; 两岁多 a little more than 2 years old 56块多，56 yuan; 56块多 a little more than 56 yuan. see? 多 in this case often is put behind the measure word