Itachi Uchiha is older than Obito Uchiha by four years. Itachi was born on September 9th, in the year 238 of the Shinobi calendar, while Obito was born on December 27th, in the year 242 of the Shinobi calendar.
This means that at the time of their final battle, Itachi was 23 years old while Obito was only 19. Even though he was younger, Obito had already accomplished a great deal in his short life. He had become a powerful ninja and played a key role in many important missions. Itachi, on the other hand, despite being older, was not as experienced as Obito. He had only recently been promoted to Jonin rank and had yet to really prove himself as a ninja.
In terms of strength, both Itachi and Obito were incredibly powerful ninjas. They were both capable of using powerful techniques that could easily kill their opponents. However, Itachi was generally considered to be the stronger of the two. This is likely due to his experience and natural talent as a ninja.
Ultimately, it is clear that both Itachi and Obito were incredibly talented and powerful ninjas. Though Itachi may have been slightly stronger overall, it is clear that either one could have won their battle if they had fought each other at full power.