What kind of learning curve could I expect if I took on a new language I have no experience with?
If you're over 40 and you don't know how to answer that question based on past experience, I think you're in trouble. Picking up new languages, frameworks, APIs, and what have you are just par for the course. Those things have been a constant in every development job I've had. If a language is related to something that I already know, then within a few weeks, I may be writing some Perl-ish looking Python and becoming more comfortable using constructs that don't appear in Perl very quickly.