Typically what we call hour building is that bit between your Private pilots license and Commercial pilots licence should you do a modular route. In other words a typical modular route should look like this:
First 50 or so hours - PPL,
Night Rating (5 hours)
Hour Building (100 hours or so) (in the mean time you study ATPL theory)
the minimum experience you need to have before starting a CPL/ME/IR course is 100 hours as Pilot in command and 150 hours total time. However to sit a CPL skills test you will need 200 hours. (only 5 can be credited from a simulator), that typically means if you walk in to your CPL course with the bare minimum of 150 hours, you will not have enough as most schools will finish CPL/ME/IR training in just 40 hours or less.. My advice - find out the requirements of the school you will choose and make sure you have enough hours before starting the course.
That's to describe a modular path.. Integrated is a bit different
after CPL/ME/IR you do your MCC and start sending your CVs
as for the age - one of my friends is starting his Type Rating with Turkish Airlines shortly at the age of 41. He is part Turkish so that might have helped him a bit. 40-ish is not too old, but I would suggest it's the last point at which you can jump in the train.
One last bit I want to mention - there are some Eastern European schools out there that appear cheap simply because they only include Single Engine instrument rating in their package. Some are even being naughty and try to conceal this fact by throwing a MEP rating in the mix to confuse you. Make sure the rating you will end up getting is indeed a multi engine instrument rating, as this is what you will need to begin a type rating on a multi engine aircraft. Some people have been burned on this - they sign up, start the training and as they go they are told that the original price they were quoted for is for SE-IR only, and to get a ME-IR the price you are then facing is the same as in Ireland/UK