75 lbs is very much possible if you have a large, skinny frame (like I did). If you perfect your training & eating, you should be able to put on 100 lbs of lean mass. I plan on gaining the 100 lbs mark by the end of august (my 22nd birthday).
You obviously have a lot to learn, but here is a little advice for you: you need a little over 1000 extra cals per day. I make a pre and post work out drink at 1000 cals each (N-Large2 "gainer", litre milk, couple bananas). If you take this directly before and after your workout it won't come on as fat. Rest of the time you gotta stick to complex carbs. Also, take every set to failure and train 5 days a week. These are probably the two most crutial parts of my routine. You have a lot reading to do, but don't be discouraged by somebody's aribitrary limitations on what YOU can accomplish in a year.
If you are already at or near your genetic potential I doubt you can put on 100lbs of anything other than fat in one year.