45 and Too Old to Work?

The title is from (and linked to) a Ziff Davis article about the difficulty that more experienced tech workers can have finding a job. He cites a "friend" who at first had no luck job hunting, then had much better luck when he reduced his age to "indicate that he was in his 30s". The author doesn't understand why companies would prefer to hire younger, less experienced workers who are less likely to keep the job for a long time. I'll venture some hypotheses:

• They can be paid less.
• They will happily work longer hours (tech ennui hasn't set in yet).
• They have fewer family commitments (less time off/lower benefit costs).
• They are less independent/easier for their bosses to control/less threatening to their bosses (who, after all, are likely the ones doing the hiring).
• Companies don't want to "over hire": they prefer mediocre employees who will be happy with their jobs than someone "over-qualified".