First off, welcome to the forum, you will find a lot of useful information here.
To answer your first question, no, you are not too old to start training in MMA or going for a career.
You should search for local gyms around your area to join. You should probably start off slow, as wanting to train and actually enjoying the training are two different things.
Good luck, hope you do well.
“Anna, my strong, terrifying Anna.” -Cas
"You lack the requisite spine and testicular fortitude to study under me" -Elodin