At first I thought level 25 was reasonable because legacy level goes up very fast doing dailies, but then I found out that the exp required for a level starts increasing quite dramatically from level 20 onward so its quite a lot of work.
Yeah I have 2 lvl 50's, one of which I have been using 2-4 hours a day doing PVP and Black Hole - Ilum Dailies, and I am only at Legacy 21, now I gimped myself a little by a. rerolling my main like 3x (for stuipid reasons like I didnt like his name or skin) so it took me a long time to actually start accruing legacy xp and b. I pvp a lot so I am always over leveled on my class quests (meaning until the 50 dailies the ONLY legacy xp I earn is from PVP)
All that to say, I am a dude who has played this game between 1-3 hours a day and 4-6 on weekends pretty much EVERY day since launch. I feel like I should be a lot higher in Legacy. Maybe if they just made so legacy xp never gets nerfed i.e. you get normal legacy xp for killing gray mobs, even if you get no actual xp.