You can use the key option of the sort command, which takes a “field number”, so if you wanted the second column:
sort -k2 -n yourfile
-n,--numeric-sortcompare according to string numerical value
For example:
$ cat ages.txt
Bob 12
Jane 48
Mark 3
Tashi 54
$ sort -k2 -n ages.txt
Mark 3
Bob 12
Jane 48
Tashi 54