Marek Pulling Up

I'm not sure why Marek is trying to grow up so fast - I really wish he'd slow down! He's really not happy just sitting anymore - when I try to put him down he straightens his legs. I have to almost lay him down and then try to force his bottom down to get him to sit! He only wants to stand and "walk" with me holding him. When he is sitting he's already trying to pull up onto everything. Thankfully, he still prefers to be held most of the time. Although he is quite heavy . . . I caught him on video pulling up onto his little table - by himself - and walking his feet in. He's getting so big!