Rather than "you're never to old! follow your heart!" cheerleading, it would be a lot more useful to hear HOW the author deals with the the array of commitments the average 30-40 year old person has. Mortgage, day care, insurance, kid commitments etc.
Stopping work and having what ajg1977 states - "Mortgage, day care, insurance, kid commitments etc" - is the battle. Many successful startups have an average "age" of around 26 which seem to be [from some Y-Combinator article I read] the age when startups succeed for a whole raft of factors [age, martial status, flexibility, financial security, maturity etc etc] - there's always an exception to the rule however.
If you >30 - nothing's stopping you but yourself. The question often answers itself however - most >30 stop themselves due to externalities.
*but best of luck :P