...but Appendix B states that Aragorn was born in 2931, Bilbo went off to Erebor in 2941, and in 2956, "Aragorn meets Gandalf and their friendship begins."  In 2957-80 it states that "Aragorn undertakes his great journeys and errantries" in Rohan and Gondor.  It is known that when he was in Gondor, serving under the Steward Ecthelion as "Thorongil," Gandalf supported him, much to the annoyance of Ecthelion's son, Denethor, who was Aragorn's rival.  Aragorn and the Rangers also kept watch over the Shire at Gandalf's behest; he also tracked down and captured Gollum at Gandalf's request.  And Aragorn in Moria said to the hobbits that he had been on many a journey with Gandalf, if none so dark, and that there are tales in Rivendell of greater deeds of his than any Aragorn had personally seen.  But I believe that is pretty much the extent to which anything is known about their adventures together before the War of the Ring.

Watson's TTT Review