I believe, the realistic life of a T5HO bulb is about +/- 9 months, and they drop off dramatically as they age. So while some push their lifespan to a year or so, others will swap them out at 6 months. A lot depends on your goals.
If you're just keeping fish for now and not planning on anything that requires light for photosynthesis, you don't need any special lighting at all. So if the T5s you have now still throw enough visible light that you can see your fish and you're happy, don't sweat it. If you want to grow corals or anything else that needs light to survive, then yes, you are best off to replace your T5 bulbs from 2007 ;-)
As others have said, you cannot *see* the light that is needed by photosynthetic organisms. It's best to use a PAR meter, or just change your bulbs regularly, somewhere around every 9-12 months or so.
As always, best of luck with your build!