Hi @anabel and welcome to the wonderful world of house and pet sitting.
I completely agree with what @Cuttlefish and @Amparo say, both experienced sitters and world travellers.
Why don’t you attach your profile to your forum profile so that we, and other members, can have a look and give advice if we feel it needs improving? Here’s how:
Make sure when you apply to sits that you personalise each application, including the names of the animals and mentioning the experience you have with such animals and maybe an anecdote or two. You must treat each application just like you would applying for a job.
Age is just a number, so don’t fixate on that.
Good luck!