A Game of Tag?!

'A game of tag!', said he to me.
Blinking with incredulity,
Pressed closed my book, put up the pen
And fixed a blue-flecked eye on him:
'My lusty friend you should well know
This pensive one will rarely show
Such vigor in his worldly frame;
Yet, if this still remains your aim
Seek but the shortest breadth from thee
Ask Tanya for vivacity.