<?php

$string = "Hi, my name is Bob. I m 19yo and 170cm tall";

print_r(preg_split("/(,?\s+)|(\w\d)|(\d\w)/", $string));

Array
(
    [0] => Hi
    [1] => my
    [2] => name
    [3] => is
    [4] => Bob.
    [5] => I
    [6] => m
    [7] => 
    [8] => yo
    [9] => and
    [10] => 
    [11] => 
    [12] => m
    [13] => tall
)