Son still not walking

My son was born Dec 31 and he was about 5 weeks premature. He has hit all his milestones on time except for walking. He won’t stand by himself and he just cruises around furniture. He started this around 11 months. Everyone keeps telling me that some kids walk later and it’s normal, but we are worried. The doctor said to wait another month and then maybe we should try early interventions.

Also, he’s extremely cautious and I think this may be part of it. He’s very smart though and doesn’t have any cognitive delays.

Any thoughts? Should we be worried?