Today I was in German class and I had an epiphany when it comes to the -ty suffix we use with our numbers from twenty on. Here was my thought.
In German, they take the number such as zwei (two), drei (three), vier (four), etc and they add -zig resulting in zwanzig (twenty), dreissig (thirty), vierzig (forty), etc. The -zig/ suffix is really quite interesting because it must come from the word zehn and a temporal indicator -ig, identical to the Greek -ακις which tell you how many times. To use an example from Greek where this temporal indicator was common πέντακις (five times). Originally, the -zig suffix must have been a longer form such zehnzig (ten times) to which you tacked on a number. So, for example, zwanzig (twenty) must have originally been zweizehnzig (ten times two) which is simple multiplication, just in terms of language.
So, to return to English from German and the -ty suffix inherent in our numbers, it's helpful to consider the old English twentig (twenty), þritig (thirty), etc. It is the same case as in German. At one time, people might have said twotenig for twentig. As time went by, the velar consonant g disappeared leaving us with the -ty suffix.