Can we use the word "coed" to describe any activities or facilities available for both men and women, or should it only be limited to something educational or youth related? Also, any suggestions for alternatives?
‘Coed’ is a contraction of ‘coeducation’ or ‘coeducational’, specifically referring to the teaching of males and females together. (See Merriam-Webster.) In the present-day this might seem a redundant term. In western culture it became significant in relation to the women's movement (this Wikipedia article provides some context), and the growing access to (notably higher) education for girls.
(The term is typically associated with youth, incidentally, but it need not be: students can be any age.)
In principle there is nothing to stop you using the word for realms beyond education, in the same way that the word ‘ecumenical’ originally signified relationships between religious communities, but is now used simply to mean even-handedness across any boundaries. The ‘ed’ part is a bit on-the-nose, however, and could make such usage seem rather forced.
One alternative (as the Wikipedia article makes clear) is ‘mixed-sex’. Slightly less awkward is ‘unisex’, which tends to indicate an active concern not to discriminate between the sexes.