Material UI Select – Change Select size

Try using size=”small” attribute on FormControl

<FormControl variant="filled" size="small">
    <InputLabel id="demo-simple-select-filled-label">Age</InputLabel>
    <Select
      labelId="demo-simple-select-filled-label"
      id="demo-simple-select-filled"
      value={age}
      onChange={handleChange}
    >
      <MenuItem value="">
        <em>None</em>
      </MenuItem>
      <MenuItem value={10}>Ten</MenuItem>
      <MenuItem value={20}>Twenty</MenuItem>
      <MenuItem value={30}>Thirty</MenuItem>
    </Select>
</FormControl>