Which model of the universe gives the youngest age for its present size and expansion rate?

It is called a re-collapsing universe

Explanation:

The geometry of the universe is, at least on a very large scale, elliptic. In a closed universe, gravity eventually stops the expansion of the universe, after which it starts to contract until all matter in the universe collapses to a point, a final singularity termed the "Big Crunch", the opposite of the Big Bang.

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