x <- data.frame("SN" = 1:7, "Age" = c(21,15,22,33,21,15,25), "Name" = c("John","Dora","Paul","Alex","Bud","Chad","Anton"))

x[order(x[, 'Age']),]

SN Age  Name
2  2  15  Dora
6  6  15  Chad
1  1  21  John
5  5  21   Bud
3  3  22  Paul
7  7  25 Anton
4  4  33  Alex

SN Age  Name
6  6  15  Chad
2  2  15  Dora
5  5  21   Bud
1  1  21  John
3  3  22  Paul
7  7  25 Anton
4  4  33  Alex