It's really hard to say. A lot of babies hold on to stuff for a long time, but don't take their first solo steps early.
I worked as a portrait photographer, and there were a lot of infants who were regulars, and many of them went from crawling to pulling up and creeping really quickly, but even at their one-year birthday portraits, they had to hold onto something.
MY son was late on EVERYTHING (and I do mean big-time late), and we ended up getting him one of those little cars with the high back that can be ridden on or pushed from behind, and it helped him get around, but still feel like he was holding on to something solid.
Just be patient.
Also, keep in mind how futile it is to give much thought to how soon he'll be doing everything. They develop at different rates, and in different skills. So your son might have mastered crawling and pulling up, but then take a break from learning gross motor skills in favor of improving his verbal or fine motor skills, then come back to walking later. We can help them in some ways, but when it comes right down to it, we have no control over when our kids reach developmental milestones, so as long as he's not severely late in something, wondering and worrying won't make a difference.