UESP says the hard cap is 70 as that is what you would be when all skills are 100.
I suppose it depends on what race you are, because obviously starting with fewer skill points would allow one to reach higher levels.
Too bad going to jail only reduces the progress on a skill and not the skill itself so you could theoretically have an infinite number of levels. Suppose they did that to prevent people from making a toon with every single perk
