Haha I basically stumbled upon my answer as I was trying to figure out what the right equation is 

That's correct, but again there is an equation to be found and solved :)

There are two points in time, now and then.

We define $$x$$ as Jimmy's age now.
"Then" is when Tom was $$x$$ years old.

| Person | Now | Then |
| ----- | ----- | ----- |
| Tom | 24 | x |
| Jimmy | x | |

To get from now to then (reading Tom's line) we subtract 24 and add x, hence the bottom right cell is $$x-24+x = 2x-24$$.


| Person | Now | Then |
| ----- | ----- | ----- |
| Tom | 24 | x |
| Jimmy | x | 2x-24 |

Now the equation is simply $$2 \times (2x - 24) = 24$$, or $$x = 18$$.


Scroogey

Jimmy was 12 when Tom was as old as Jimmy is now.

Thus, Jimmy is 18 now, because 6 years ago Jimmy was 12 and Tom was 18.

science

Secondary school math puzzle

Jimmy was 12 when Tom was as old as Jimmy is now.

Thus, Jimmy is 18 now, because 6 years ago Jimmy was 12 and Tom was 18.

I did guess and check again, haha.
