Is there any possibility you could post a photograph - I'd like to see where its growing and what shape its forming. And I'd ask if it gets plenty of sun. And do you feed it or not, if you do, what with?

This is a topic we have discussed before and lots of people have had Wisterias that never flower. Some GOY members have had theirs like you for many years. The only way to be sure is to buy one already in flower in the Spring. I did this and mine flowers every year. It is a great joy to me and well worth having.
Best wishes
Linda

This link showing how and when to prune might help you. According to the link which is RHS advice a wisteria grown from a seedling can take 20 years to flower. They also advise careful watering at this time of year as that can be a reason why you do not get flowers. They are also susceptible to early spring frosts damaging flowers before they open andcausing early dropping of flower heads. http://apps.rhs.org.uk/advicesearch/Profile.aspx?pid=242

Well it sounds like Meatymaximus is pruning at the right times, but it may be that there are too many mainstems and the plant's not been trained properly. After 25 years, it should be possible to get it to flower, but I'd still like to see what it looks like to tell you what I'd do, and the info I asked for initially - I have one in a client's garden which is 15 years old, never flowered, but I got it to perform for the first time last year, so I think it's worth a try with yours.