no, I do not know of any way to tell the sex of a juvenile trachycarpus before it produces flowers stalks.
However, even if it produces flowers for the first time this does not necessarily mean that it keeps this sex.
Trachycarpus (fortunei) can produce male flowers first and after having established better suddenly produces female flowers.
Or vice versa, if the growing conditions have deteriorated a formerly female plant can switch to male.
Moreover, fortunei (and Takil the Rome one) can suddenly start to produce hermaphroditic flowers apart from their normal male or female flowers.
Thus male plants can appear to be female although they only have produced some hermaphroditic but fertile flowers which eventually produce fertile seeds. This is currently happening with the true Takil in Rome.

So are you saying that a takil with good growing conditions ( abundant water, lots of sun, lots of nutrition ) will most likey be a female and a takil growing in less favorable conditions will be a male ( less water, partial shade, and less or no fertilization ) ? If so then wouldnt it be possible to have to crops in a nursey one favorable for growing males and one favorable for growing females. Or has this been done already? I know I have heard of such thing through out nature such as cooler temp in a human male will create xy sperm and hot temps will create xx sperm or in crocodiles the temp of the egg directly effects the sex of the embryo.

no, that´s not what I´m saying. However, the chance to get a palm with female inflorecence is higher if it is well established and well fed and watered. There is no difference in this with takil and fortunei. By the way I personally believe that the "takils" that grow here nowadays are fortuneis anyway. Just take a close look at the leaves. They are deeply split.

less water, less light, less wamth and less nutrition puts a plant under stress and this CAN result in a change of the gender of the flowers.
Remember, it is far more energy consuming for a plant to produce fruits than male flowers which drie out later and won´t have to be fed any longer.

The true sex of a palm is normally fixed in its genes but Trachycarpus has found a way to outsmart the genes. It also can change from female to hermaphroditic flowers if it has not been pollinated for a long time. Thus it can produce seeds and offsprings even if no male palm is available for pollination. A very useful trick if you bear in mind that Trachycarpus is mainly spread by birds dropping a single seed somewhere.

As regards takil there seems to be a problem with female flowering. Beccari produced several Takils from the batch of seeds he got from Kumaon in 1887 but all of them were male. When he wrote his description of T. takil it was therefore based on male specimens only. He waitet four more years but none of his takils turned out to be female. Therefore he asked somebody in Kumaon to send him dried female flowers so that he could finish his Takil description. And even today, there are not many female Takils in the Kumaon hills and they do not flower every year. Maybe there are NO pure female Takils at all and the seeds on that trees in Kumaon are produced by hermaphroditic flowers, just as it ihs happening now in Rome with the true Takil there. Old reports say, it has done this before already burt usually it is a male.
When Beccari made his description of the femal takil flowers he found these to be almost 100% identical with female fortunei flowers.