To unlock the Fired Up trophy in The Sims 4, you will need to reach level 10 in the Fitness skill.
The quickest way to reach level 10 in the Fitness skill is to buy the three Fitness books which will bring you up to level 9, and then buy gym equipment/go for a jog and keep doing it until you complete the final level.
Once you reach level 10 in the Fitness skill, the trophy will unlock.