Hi am 27 yrs old and have a lower heart valve that is part closed. Can that cause a heart attack or a stroke? Or am I to young to have any of those?

Which valve? Don't know what a lower valve is. A stenotic valve can cause increased strain on the heart. Depending on the cause of the stenosis, damage to a valve could predispose to propagation of emboli which might cause blockages to the arteries of any part of the body. There is no age that is too low for a stroke or heart attack.
? Not sure what you mean by "lower heart valve" but heart valve disorders in 26 year olds are not likely to cause heart attacks or strokes.