No, it’s not ok. One needs a lot of bracha and siyata dishmaya for dating and for marriage, I don’t think that deception and potentially hurting your older sibling is the best way to bring that bracha into your life.
That said, although I know that some communities would never skip and marry kids out of order, I personally don’t feel it is right to hold back younger siblings when older ones have not yet gotten married, since then the younger siblings might have a hard time getting married if they wait and miss out on the prime dating years. But it has to be done with sensitivity, and with the permission of the older sibling and parents.