Starting a 1st level character won't be much issue if you award more xp to the character than his higher level party members. For example I would treat the character as two members when dividing xp to the party if there is at least 3 level difference. If there is at least 6 level difference then I would make the guy count as 3. In other words, my xp division will always be biased towards the low level guy. More than 6 level difference is indeed huge, so I prefer to have the player start from milestone levels like 3 or 5 or 9.