I've said it before and I'll say it again - if a keeper is good enough, it doesn't matter what his age is.
Look at keepers like Akinfeev, Asenjo, De Gea, Neuer, Adler, even Hart who have got into their respective first-teams at young ages and how well they've progressed.
Now is the perfect time for Szczesny to be No. 1 - he's been at the club nearly 5 years now and shown his ability at the highest level.
We certainly need decent backup though.