By "soon" I mean early - too early in the character's career. 150 XP is not very much. It's half of one Specialization tree, without spending anything for Force Powers.
For example, take a character that starts as a Pathfinder. In the Pathfinder tree the character will likely want Force Rating (at least 65 XP) and Dedication (at least an additional 100 XP) barring any other concerns. So there's 165 XP, before getting any additional skills, powers, or Force Trees. A Force Tree will cost 20, so let's be extremely focused and say 185 XP is the minimum this character would need to get Lightsaber as a Career skill.
I know some will say, "Just get the second tree early." I think that having Lightsaber as a Career skill would be a necessary part of being called a "Knight" (what's a knight without a sword? we call that a jockey), it is not sufficient for the title.
And in any case, that's an extremely narrow focus. I think that Knight level should be higher, in fact I'd say 300 XP, since that's exactly every talent in a specialization tree, and since every talent isn't necessarily going to be taken, the rest can go to powers and additional trees.
There aren't a lot of good constants floating around in this game (which is good), Force Power Trees aren't required to follow a cost chart the way Specialization trees do, and it makes it difficult to come up with a good quantity. 150 is definitely too low, laughably too low (I laughed, so did my GM and another player).