Hosea 5:6 (NIV)
When they go with their flocks and herds to seek the Lord, they will not find him; he has withdrawn himself from them.
Technically, it is never too late to come to God in repentance and faith to be saved. But practically speaking, too late is indeed too late. Think about it, everything is going just fine and all of a sudden the plane starts to go down. You've only got less than a minute. What do you do? Cry out to God of course. But how can you possibly muster up saving, trusting, loving faith at that moment?
God is not a parachute.
Proverbs 27:1 (NKJV)
Do not boast about tomorrow, For you do not know what a day may bring forth.
2 Corinthians 6:2b (NKJV)
Behold, now is the accepted time; behold, now is the day of salvation.