my son is 15 months, he's just started running the last week & only started walking a few weeks before that LOL
He says one word at a time, mama, dada, car, ta etc
He does understand some instructions, I ask him where his dummy is "where's your dummy? Get your dummy & come to mummy" He looks for his dummy, gets it, puts it in his mouth & comes to me. He also understands when I say sippy cup or toy car in relation to that.
He gets the remote or the phone & presses random numbers until I take it off him LOL & he likes turning lights on & off (also turning the vacuum on & off grrrrrr)

It sounds to me like your son is doing well. They all catch up to each other around 2-3 yrs old anyway so I definately wouldnt be worried about what he is or isnt doing at this point in time (unless it was something like not sitting up or rolling over etc by 12 months, that may need to be investigated?)
Just sit back & enjoy all the cute things he's learning... before you know it you'll be kissing his cheek & sending him off for his first day of school (sniff,sniff)