Poops, I'm not going to argue with this one. I freely admit my experience with and understanding of exercise and nutrition isn't as deep as yours. I stand by my original opinion that light lifting might be a fun thing to get into, but significant changes in body mass through exercise should wait until later in puberty. As well, I still believe a variety of ab exercises are necessary to fully develop the area, because I've found for myself that crunches simply do not develop the full range of the muscle.
My only real issue is that clearly the original poster does not already go to a gym or know someone who does, otherwise he'd be asking that person and not us. Consequently, this concerns me as to how he's supposed to find out the proper form, so advising what can be complicated exercises to perform initially (squats and deadlifts) might end up in him researching the form online, misinterpreting something, and consequently screwing things up. IMO, more complicated exercises such as that should wait until you're more experienced in the gym and have someone who really knows what they're doing to go through the full exercise with you.
My only real issue is that clearly the original poster does not already go to a gym or know someone who does, otherwise he'd be asking that person and not us. Consequently, this concerns me as to how he's supposed to find out the proper form, so advising what can be complicated exercises to perform initially (squats and deadlifts) might end up in him researching the form online, misinterpreting something, and consequently screwing things up. IMO, more complicated exercises such as that should wait until you're more experienced in the gym and have someone who really knows what they're doing to go through the full exercise with you.