[r] R * not meaningful for factors ERROR

I have the following data.frame and I want to perform some calculations on the 2nd column.

> test  
  code age
1  101  15
2  102  25
3  103  16
4  104  u1
5  105  u1
6  106  u2
7  107  27
8  108  27

As you can see, the 2nd column does not include only numbers. I omitted these cases:

> new<-subset(test,code<104 | code>106)
> new
  code age
1  101  15
2  102  25
3  103  16
7  107  27
8  108  27

But when I try to do a calculation in a new column this is what I get:

> new["MY_NEW_COLUMN"] <- NA
> new
  code age MY_NEW_COLUMN
1  101  15            NA
2  102  25            NA
3  103  16            NA
7  107  27            NA
8  108  27            NA
> new$MY_NEW_COLUMN <-new[,2] * 5
Warning message:
In Ops.factor(new[, 2], 5) : * not meaningful for factors   

Why does that happen? Any suggestions?