hhmm - when dd started walking there were times when she'd revert to crawling because it was quicker and she was more confident - it only lasted a few weeks though.
The average for walking is 14 months - some will be quicker / some slower, DD walked at 14 months but had stood (once) unaided at 10 months and cruised for months.
We were under the community children's physio for something else entirely but she told me that they don't consider it to be late until baby is 24 months and not walking. So if i were you i'd leave it another few weeks and then if your still worried ask your HV/GP for a referral to your local children's physio - they can rule out any problems and show you exercises etc to help.
dd is just 16m. she has been cruising holding on to furniture for months and a few weeks ago learned to stand up without holding anything and eventually this led to her taking a few steps unaided. she was so excited. she can at times stand up and walk thru the whole house but as time has gone on she just does it less and less, always preferring to crawl or walk on her knees. is this normal? i thought once she was off there would be no stopping her but its the opposite. some days she doesn't attempt to walk at all and if i stand her up and encourage her she just reverts to crawling!