Return Max or Min value based on criteria

My first post. Have searched quite a bit, but not finding 'exactly' what I'm looking for.

ColA
1
1.1
1.1.1
1.1.2
1.2
1.2.1
1.2.2

ColB
5
10
15
20
25
30
35

I want to be able to look up and return min or max values based on matching left "x" number of string characters, where "x" is based on the length of the string I entered.

Entries would return results as follows (for max):

1 would return 35 (because all criteria values start with 1).
1.1 would return 20 (max of items starting with 1.1).
1.1.1 would return 15.
1.2 would return 35.

Appreciate any help.