Хранить состояние пользователя. Таблица users:
login | state | name | age
------------------------------------------------
vasya | new | NULL | NULL
petya | waiting_for_name | NULL | NULL
vanya | waiting_for_age | Иван | NULL
misha | all_data_given | Михаил | 46
набросок кода для понимания:
if ($current_user_state == 'new') {
echo 'What\'s your name?';
setCurrentUserState('waiting_for_name');
} else if ($current_user_state == 'waiting_for_name') {
echo 'Hello, ' . $user_message . '!';
setCurrentUserState('waiting_for_age');
} else if ($current_user_state == 'waiting_for_age') {
echo 'Oh, you are ' . $user_message . '! You\'re so damn old';
setCurrentUserState('all_data_given');
}