可以使用Sub()函数计算两个时间之间的差异，然后使用Years()、Months()和Days()函数来获取相应的年、月和日数。以下是一个示例代码：

package main

import (
    "fmt"
    "time"
)

func main() {
    now := time.Now()
    birthdate := time.Date(1990, 1, 1, 0, 0, 0, 0, time.UTC)

    years, months, days := diff(birthdate, now)

    fmt.Printf("Age: %d years, %d months, %d days\n", years, months, days)
}

func diff(birthdate, now time.Time) (int, int, int) {
    years := now.Year() - birthdate.Year()
    months := int(now.Month() - birthdate.Month())
    days := now.Day() - birthdate.Day()

    if months < 0 {
        years--
        months += 12
    }
    if days < 0 {
        months--
        days += daysInMonth(now.Month()-1, now.Year())
    }

    return years, months, days
}

func daysInMonth(month time.Month, year int) int {
    switch month {
    case time.February:
        if year%4 == 0 && (year%100 != 0 || year%400 == 0) {
            return 29
        }
        return 28
    case time.April, time.June, time.September, time.November:
        return 30
    default:
        return 31
    }
}