Age Calculate from Date In LWC

Agecalculator.html

<template>
    <lightning-card  title="Age Calculator">
        <lightning-button variant="brand" label="Calculate"  slot="actions" onclick={calculateDOB}></lightning-button>
        <p class="slds-p-horizontal_small">
            <lightning-input type="date" name="BirthDate" label="Enter Your Date Of Birth" placeholder="type here..." value={birthdate} onchange= {handleChangeNum1}></lightning-input>
            result---{result}
        </p>
    </lightning-card>
</template>

AgeCalculator.js

export default class AgeCalculator extends LightningElement {
    @track result;
    @track birthdate;
    today = new Date();
    handleChangeNum1(event){
        const inpurdate = event.target.name;
        const inputvalue= event.target.value;
        if(inpurdate=='BirthDate'){
            this.birthdate=inputvalue;
        }
    }
    calculateDOB (event) {
        this.result=today.getfullyear-this.birthdate.getfullyear;
    }
}