DD1 took her first steps at 7 months and was competently waking outdoors and everywhere by 8 months. She skipped rolling and crawling completely.
She learnt to sit unaided at 6 months, having never rolled. Then within 2 weeks if she was sat by the side of a surface (like the sofa) she could pull herself to standing. Cruised for a week (literally just a few days) likewise stood unaided for a couple of days. Then aged 7 months and 2 days took 2 steps from Sofa to her Nana. Walking fully within a week.
I guess that by 7 months she was of an age when most babies want to move. Most roll around, 'caterpillar', commando or crawl to get from one place to another. DD1 never learnt any of these things. So her moving was learnt on her feet.
She was under paediatric referral by aged 2 for bow legs - direct consequence of walking before her bones were developed enough to take her weight. So it's not all good 
My other two children, however, walked at a more normal 11 months old. They didn't by-pass crawling like their big sister.