As @Lighthart noted, not that many Time Lords left Gallifrey as a matter of course to begin with, so there wouldn't be that many of them swanning about anyway. And with the whole of spacetime to romp around in, that's a lot of wherewhens to contend with, so the chances of running into another Time Lord purely by chance would be extremely slim.
But more central to that, I think, is that Gallifrey tends to be internally consistent, time-wise. That is to say that the "clock in San Dimas is always running," as it were. It's impossible, for instance, for the Doctor to go back to Gallifrey at a point in time before the Time War, for instance, because it's crossing his own timeline. (Yes, I know, it happens in Listen. But that wasn't the Doctor, and Clara is -- sigh -- the Impossible Girl.)
This would keep Time Lords from meeting each other out of order, except under very exceptional circumstances. The possibility of paradox becomes too great otherwise. Imagine if the Eleventh Doctor he were to meet, say, the Third Romana, and warn her about the Time War. That could radically alter what would, presumably, be a fixed point. And we've seen what can come with mucking about with fixed points. (There's an Eighth Doctor novel where he receives a distress call from Susan and, rather than responding, tries to track it back temporally to rescue her before she sends the call. He encounters the Master at an earlier point in his timeline and winds up creating the very circumstances he was trying to prevent -- effect precedes cause.)
So, since all the Time Lords are moving forward in time at the same rate relative to Gallifrey (or, possibly, relative to the Eye of Harmony, if I may speculate a little), then no matter where the Doctor goes, the Laws of Time will prevent him from landing in a wherewhen that would bring him into contact with an earlier version of a Time Lord.