The stories of Hal's irresponsible youth are not present in Holinshed, but they are not Shakespeare's invention, either. Hotspur became a such a impetuous sort who always wore his heart on his sleeve to better contrast with Prince Hal, a very cold, calculating young man whose true motives were always kept a secret from those around him. Nowhere in the source material is it suggested that Hotspur was so impetuous as he is in 'Henry IV', although his nickname, Hotspur, may have suggested this impulsive nature. Hotspur is impatient with Glendower's 'skimble-skamble stuff' (3.1.156), and seems to be uninterested in details, such as when he forgets the map in Act III.i, or his reluctance to read letters during Act IV.i.
Other than his age, the only major change which Shakespeare makes to Hotspur is his rashness and temper.
Historically, Hotspur seems to have been everything the fictional King thought him to be, a brave fighter and competent leader.
