Get person's age in Ruby

I'd like to get a person's age from its birthday. now - birthday / 365 doesn't work, because some years have 366 days. I came up with the following code:

now = Date.today
year = now.year - birth_date.year

if (date+year.year) > now
  year = year - 1
end

Is there a more Ruby'ish way to calculate age?

I know I'm late to the party here, but the accepted answer will break horribly when trying to work out the age of someone born on the 29th February on a leap year. This is because the call to birthday.to_date.change(:year => now.year) creates an invalid date.

I used the following code instead:

require 'date'

def age(dob)
  now = Time.now.utc.to_date
  now.year - dob.year - ((now.month > dob.month || (now.month == dob.month && now.day >= dob.day)) ? 0 : 1)
end

I've found this solution to work well and be readable for other people:

    age = Date.today.year - birthday.year
    age -= 1 if Date.today < birthday + age.years #for days before birthday

Easy and you don't need to worry about handling leap year and such.

Use this:

def age
  now = Time.now.utc.to_date
  now.year - birthday.year - (birthday.to_date.change(:year => now.year) > now ? 1 : 0)
end