I wound say they are the same ,asking for age.But for me as a Chinese speaker ,i will use each of the sentence when..~>

你多大了？will be more suitable when u ask a person look yonger than u .

多大年纪-ask a person who look older than u

几岁-anyone or the person u ask has similar age with u (most common to use)

多大岁数-ask to a person much older than u(not common to use )

Hope thsi will helpful ;)

It's an interesting question, I totally agree with Gracie about when and how to use them respectively, This also reminds me that I've once watched an award ceremony on TV and heard a celebrity from Taiwan ask an elderly people 你几岁了？ on stage, I was actually a bit shocked at the moment and thinking about why he'd ask 你几岁了 when 您(今年)多大年纪了? could've been much better and appropriate, but shortly after, I suspected we might be in the realm of differences between one country's stylistic preferences and another's. However, after reading Gracie's post, an insight from Malaysia, we're obviously on the same page. So, I'm not here trying to be a nit-picker, also no offence intended. Or the Taiwanese celebrity might have just worded it wrongly and it's simply an exception, but just out of curiosity, do you ask 你几岁了 to people of all ages in Taiwan? I mean, even to an elderly people? It'd be appreciated if I could get some voices from friends in Taiwan.