Are these pigeon eggs too old to candle?

[ilikepigeons]

I got two new pigeons, was told 4 months old and that they're Birmingham Rollers. They laid a clutch on the 25th and 26th of January. I don't want to fly them until they've raised this clutch (if it is fertile) but it does interfere with their set release date a little as it's right in the middle of incubation. I don't want to keep them sitting there for nothing if the eggs are not fertile. If they actually are that young (I'm not sure if you can tell age from looking at them? I could post pics if that would help) I'm not sure they actually would be fertile. I reckon one is a male from behaviour and obviously I have a female, I have seen the male what appears to be courting my female through the coop but I have never actually seen him court or mate the female that laid eggs. I suppose they could have done it in private though.
I'd like to candle them to see if they are fertile, but I have heard you need to candle on the 3rd to 5th days only from a dodgey online article. It's the 6th and 7th day for these eggs, is it too late? I have literally no idea of how to candle eggs except you hold the egg under a bright light in a dark room. I could post pics of the egg being candled here if I could get some ones more experienced opinion.

 

[Pyxis]

You can candle. It's the same as you would do for any other type of egg - in a dark place, hold the light to the air cell end of the egg (that side will be the rounder side). If they're developing, you'll see veins and the embryo.