I'm a 30 years old male 5'7" and currently 135 lbs with about 10% or less body fat, mostly over my abs. I was 195 lbs two years ago (pure fat.) I'm curious if I tried to gain lean mass, how big could I reasonably get eating strict paleo, without the use of artificial hormones? How big could I get 1 year, 2 years, 5 years from now? What would the optimum calorie intake for a person my size to gain lean mass?
OK, I feel pretty equipped to answer this; I’m 31 years old, 5’11” and currently 176.5 but when I started lifting (while always paleo) I was 154. This growth has occurred over 9 months. I have never in my life touched an artificial or natural hormone.
You can get as big as you want with strict paleo. Paleo will in no way hinder your progress. What will hinder your progress is
I have to ask where do you get this ten percent or less BF? Scales with BF percentages should be disregarded. This is the best tutorial regarding BF percentages I have come across, pictures are better than numbers: http://www.leighpeele.com/body-fat-pictures-and-percentages
I have gained over 20 pounds while being strict paleo. I lift usually 3 times per week, with classic compound lifts:
Record your lifting numbers and always strive to add weight to the bar, that is the only way you will stimulate growth in your muscles. Then to fuel that stimulus you must eat a caloric-surplus to grow. For me this had been until very recently in the 2500-2700 cals per day range but I’ve only very recently moved north to 2900-3100 daily to keep growing.
Always remember that there is no mystery, there is no magic: if you continually lift progressively heavier loads and continually eat at least a slight caloric surplus you will grow stronger and larger. Very straight forward. All it takes is consistence and hard work.
Generally speaking, being stronger is more useful than being weak.
All the best.
Bodybuilding, eh? There's a rough guide of your natural lean potential here: http://www.weightrainer.net/bodypred.html
Basically it correlates with bone structure, because your genetics will determine how much you can do naturally.
In terms of how long it would take to accomplish that, years at least. Depending on who you talk to, the maximum "lean" gain possible in a year is around 10lbs of muscle. You can certainly bulk faster than that, but then you'll be gaining fat as well and you'll eventually have to diet it off if you want to be lean.
You will have to derive your calorie intake by individual trial and error over time. It will vary based on the context of your training and individual response to food. Martin Berkhan at Lean Gains has a lot of information about how to go about doing this. You'll need to eat more, obviously, but how much will depend on you.