Can I say : "I'm one seventy five", meaning that my height is 1.75 metres ?
If X is a reasonable number (say, between 3 and 100), then I am likely to interpret the following phrase as being your age:
In the UK, unless it is required for scientific purposes or to comply with a specific numbering convention, a person's height is usually measured using the imperial units of foot (') and inches (").
1m ≈ 1'3" (ie 1 foot 3 inches)
1.75m ≈ 5'9" (ie 5 foot 9 inches, or 5 foot 9, or five nine when somebody asks how tall you are).
If the metric system is used then, 1.75m becomes:
one point, seven-five meters. [note: not seventy-five]
Thus, "I'm one point, seven-five meters tall".