That is a good question. Cost and worth are 2 different things, if no one finds you worth the cost you charge per min you will make no money, that is why I am team get in where you fit in when it come to rates. Start out with the lowest rate and then slowly raise it by a small amount. At some point you will hit an amount where people either arent buying anymore or the length of your shows are shorter than usual in which case you might want to consider dropping back down to the last rate change amount.
But in general, what you charge needs to be what you are comfortable with.
Age has nothing to do with pricing . I make more than some girls half my age & a lot of ladies considerably older than me make more than I do so don't undervalue yourself. Play up the milf/gilf thing. Also keep in mind that depending on where you are located Streamate will only pay you between 30%-35%. Assuming you have a decent computer and a reasonable knowledge of fetishes I wouldn't start below 4.99 Private 5.99 exclusive. 3.99/4.99 at the absolute lowest and that is very low. I can't help you with advice on Gold Show pricing though as I've never done one.