1/2 hand. CO has a 1500 stack, pretty big for a 300 bi 1/2 game. younger kid who has been opening quite wide, raising limpers quite wide, and even 3betting much more frequently than a typical 1/2 player.

my stack is 400

preflop: mp limper, CO raises to 12, hero 3bets to 36 with KJo?

im thinking that i want a wide, linear 3betting range here vs. this type of opponent. not sure if KJo is too wide? im not sure how he will respond to aggression b/c as is typical at 1/2, nobody has responded by other than calling or folding to him so far. my assumption is that 1) his range is wide, and 2) he's going to be less inclined to fold preflop . given that, i want a wide/linear 3bet range. how wide though? KJo might be just a bit thin? and if so, its clearly good enough to call with?

How long have you been watching him? What percentage of hands he is opening? Is he opening more hands in LP vs EP? Different sizing depending on position and/or limpers?

Having some idea how many hands he is opening is a big thing here. Depending on what his LP range is KJo might be too thin but is probably slightly ahead to well ahead. It is also a hand you won't want to play for stacks post flop very often and 3 betting is inflating the pot. So raising, calling and folding are all probably in play here.

How he will respond to raises is the other thing you need to know but you are likely to learn that only through raising yourself. Watch if he is good enough to adjust to your play also. If he is decent at this he probably folds all but his really good hands the first time you 3 bet and starts paying attention to how often you are raising and playing to see how he should adjust. Most 1/2 lags call too often in this sort of situation.

This is definitely going to be profitable the first time you do it. Just keep an eye on what you think his impression of you is. With this type of young player, they are liable to turn things into a macho contest if they think you're starting to target them.

I like this better if there hadn't been a limper. I've played a lot of hands online, and I can say that 3-betting isolation raises light isn't +EV. People are actually iso raising limps less wide than you think they are.

Also, I don't think you should be 3-betting here at a 100% frequency with KJo. Your 3-betting range is going to have too many weak hands/bluffs if you're 3-betting a lot of offsuit broadways at a high frequency or 100% frequency. Mixing between folding/3-betting is probably ideal.