He probably means be aware of the old lead based paint . Usually fine if you paint over it but if you have to sand it back first ( as you should with all paint jobs ) then the dust can cause some long term health problems. There are DIY kits for testing paint for lead at Bunnings I think from memory. A quick Google confirms this... http://www.bunnings.com.au/3m-instant-l ... s_p1560254 Give the area of paint you are going to test a scrub with detergent, rinse and dry first though as being a garage, the buildup of exhaust fumes may give you a false positive when you test it.
If you do have to sand the timber or remove flaky bits then use a mask and overalls etc. At least by painting over it you will have contained the lead and it will not be exposed to the air.
If you have to sand it right back to the timber be careful as some of the older treated timber had CCA preservative in it - an arsenic based chemical. Once again not too good for your health.
Stewie