If you take good care of your windows, then, they ‘should last you a lifetime’. Good maintenance of any moving parts will be required, i.e clear any muck and apply grease where needed for things like hinges. You will also need to use a suitable product to clean and provide protection to the frames and the glass.
‘Should last you a lifetime is a bit of a broad statement’, even if you do maintain your windows and their frames, it all really depends on the quality of your glass and housing (frames and sills). If you haven’t done any maintenance in years, then you should consider speaking with local specialists who can either clean your existing windows and check them for energy efficiency. They could supply you with UPVC windows from Caterham which should be a little more pocket friendly in terms of reducing your energy consumption and carbon footprint.
If you have wooden sills and single glazed windows, then you are in even more need of speaking with a local firm to get your windows and frames checked out. You could find that your astronomical heating bills (that you may have become accustomed to) could be halved in price by making the move over to UPVC. If you haven’t maintained the windows, then they will almost certainly be costing you money, seals may need replacing, the wooden frames may have cracks in the wood and sometimes daylight can be seen coming through the housing or frame.