would be fortunate indeed if in fact you had found a match that quickly - success with pieces of the scarcity of your glass rarely happens with that sort of speed.

Regret I've zero experience with Facon de Venice style, so unable to help with further suggestions, and if no one else contributes you will need to make further investigations on your own - no idea of your location, but would repeat again that the V. & A. may well be able to help. They did at one time offer a drop in surgery once or twice a month, but whether that facility remains I've no idea.
Oddly I do have a small opalescent wine that a very experienced past member of the GMB attributed to Salviati's London production, but it's not in the sort of league of your flamboyant piece.
As to determining age, it depends much on the type of glass - pieces that are intended for use obviously show their age quicker than examples that are for decorative purposes only - we would hardly call you piece utility, so even with a century plus of wear, contact areas of the foot might remain almost pristine.
Period authenticity of your glass might depend of several factors - the auction description - the cost - how well it matches genuine Facon de Venise pieces of similar construction.
Your wine glass is from an area of collecting that's not for the fain hearted - don't know what you paid etc. - authentic wines in this style do not come cheaply, usually, which is a polite way of saying that you've jumped in at the deep end of a difficult collecting area, so don't be disappointed if at the end of the day your glass is a C20 copy and not something from the C19.
However, the main thing here is that you have a glass that you like and enjoy, so research the area, it's very interesting, and who knows you may have a winner.