How to write if statement in .tmux.conf to set different options?

I have a .tmux.conf which I use on different machines with different tmux versions installed.

I want to set different mouse options, depending on the tmux version. On one machine I have version 2.0 on the other 2.1.

I do not get his part right

if "[[(( $(tmux -V | cut -c 6-) < 2.1 ))]]" \
  "set -g mode-mouse on;" \
  "set -g mouse-resize-pane on;" \
  "set -g select-pane on;" \
  "set -g select-window on" "set -g mouse on"

When I source the file

$ tmux source-file .tmux.conf

I get this message

.tmux.conf:12: unknown command: set -g mouse-resize-pane on

The machine where I run it has version 2.1 so it shouldn't set the four options.

I want to set the four options when running tmux 2.0 or less or the one option when running tmux 2.1.

This bash statement works

$ tmux -V
tmux 2.1
$ if [[(( $(tmux -V | cut -c 6-) < 2.1 ))]];then echo $?;else echo $?;fi
1