A goal should be grounded within a time frame. With no time frame tied to it there’s no sense of urgency. If you want to lose 10 lbs, when do you want to lose it by? “Someday” won’t work. But if you anchor it within a timeframe, “by May 1st”, then you’ve set your unconscious mind into motion to begin working on the goal.
Your goal is probably realistic if you truly believe that it can be accomplished. Additional ways to know if your goal is realistic is to determine if you have accomplished anything similar in the past or ask yourself what conditions would have to exist to accomplish this goal.