Hi. My bub is 14.5 months. He only started crawling about 5 weeks ago. He never rolled before 1. Yes, very slow with gross motor. He is called a "low tone" bub with very flexy joints. He is also on the larger size (he just weighed n at 11.6kgs!). On the recommendation of our maternal nurse we have been taking DS to a kids physio. It has been great to give us exercises to help teach him how to do things. We are currently trying to teach DS how to walk, although I suspect it is still quite a way off for us.
Some of the exercises are as mentioned above. We bought a little trolley and we encourage DS to stand at it, and then slowly move it forward. We stand DS against the wall and sit infront and encourage him to do things with his hands (ie reach for toy that I have held out, or singing twinkle twinkle). We use toys we try to encourage cruising on furniture - we use dining chairs and over time we will slowly increase the gaps between the chairs. We also have to encourage him to move between, say, a chair and turn around to the coffee table behind him. Also, simply, holding DS's hands from behind (although try not to hold them too high in the air) and walk with them. We also have to encourage lots of standing and upright time by putting toys on chairs, tables etc.
Although I know he will do things at his own pace, I am now going to physio for my back so really the sooner he starts walking better for all of us smile Hope this helps.