Calculate years of age at a given date

calc_age.r

# Calculate age at a given reference date
# Create an interval between the date of birth and the enrollment date; 
# intervals are specific to the two dates. Periods give the actual length
# of time between those dates, so convert to period and extract the year.

calc_age <- function(birthDate, refDate = Sys.Date(), unit = "year") {
    
    require(lubridate)
    
    if(grepl(x = unit, pattern = "year")) {
        as.period(interval(birthDate, refDate), unit = 'year')$year
    } else if(grepl(x = unit, pattern = "month")) {
        as.period(interval(birthDate, refDate), unit = 'month')$month
    } else if(grepl(x = unit, pattern = "week")) {
        floor(as.period(interval(birthDate, refDate), unit = 'day')$day / 7)
    } else if(grepl(x = unit, pattern = "day")) {
        as.period(interval(birthDate, refDate), unit = 'day')$day
    } else {
        print("Argument 'unit' must be one of 'year', 'month', 'week', or 'day'")
        NA
    }
    
}


# Examples
calc_age("1990-06-30") # As long as the date is %Y-%m-%d formatted, it can be a character
calc_age("1990-06-30", unit = "months") # Other units available
calc_age("1990-06-30", "2003-07-12")   # Calculate age at any date
# Works for babies:
calc_age("1990-06-30", "1990-12-12", unit = "month")   
calc_age("1990-06-30", "1990-12-12", unit = "week")   

# Works for multiple reference dates, too
calc_age(birthDate = "1990-06-30", 
         refDate = seq(from = as.Date("2003-01-01"), to = as.Date("2012-01-01"), by = "year")
)

Very surprised to see these comments - guess I haven't been paying attention to Github for a few years!
I've updated the function to allow results in years, months, weeks, or days - which resolves @jenrichmond's question about 2.5 years too late.
Thanks to @ibelieveai for pointing out that new_interval was deprecated!

Thank you!!!! Had found Jen richmonds old post, continued looking, got here and just sorted out my dates in months column with minimal pain. Much appreicated!