Hi Flavio
Interesting question and yes, it is your decision in the end.  

For getting experience in Salesforce, you will need try one of two things -
1. volunteer work for a small company using Salesforce or perhaps a NFP. or
2. apply for roles with companies with large SF teams so that you can come in as the junior developer.

In both cases, I would suggest spending some time studying to get some certs such as App Dev, Dev1,Dev2 etc.  They are developer ones, but you could also pick up the Admin Cert.  These would at least help you get past the first barrier of having your CV read when applying for roles.

If you think Salesforce is your thing, an alternative would be to get a Mobile Developer role with a company using Salesforce, or perhaps reach out to a SF partner compnay to see if they need any work along that line.   If you are at least around others doing Dev in SF, then you can perhaps show that you have other skills outside mobile development.

There are some tough decisions to make, and in part it comes down to your current situation (e.g. age, commitments, marriage, mortgage etc) and where you want to be in the future years.  These are important things, as if you are a family man and the main income earner, perhaps volunteering for 3 to 6 months isn't going to work as you have bills to pay.  If you are young, single, living at home, volunteering for work experience may be on the cards.  How do you see your future?  If you are happy cutting code, and think you would still like to do it in your 50's or 60's, then either career would work.  And you will have to keep learning new languages.

I'm not sure what the career path for a mobile developer looks like, but I see it as a niche area to work which doesn't necessarily expose a lot of future options.  Mobile devs that I have worked with have been either solo contractors or in small consulting firms.  And have worked solely on the technical aspect of the project, with out much need to understand the business.  Your experience may be different.

When i consider Salesforce, I feel there are more future options,  I started as a Developer in SF (2013) and i've held roles titled as SF Admin, SF Dev, SF Business Analyst, SF Test & Release Manager, SF Project Manager.   There is a lot of scope to move if you grow bored as a Developer, and I think, working in roles that more generally expose you to the business and it's processes, there is more opportunity to show other skills, hence my working history.,  And by being exposed to more general business activities, it opens up other non-technical roles in the future such as IT Manager, Process Improvement, Project management.


Good luck in your decision.
Regards
Andrew

P.S. to give you some personal insight, i'm the other side of 50.  I "wrote" my first computer program in the early 1980's.  I've learnt (and forgotten) more computer languages (now long dead) than i care to remember.  I've been working with CRMs for just over 2 decades and for the last 7 years mainly with Salesforce, Although i've also done a Dynamics 365 CRM project during that time.  I don't "enjoy" coding like I used to, although I still do it well (IMHO).

For a list of languages i have learned and used over time:
Assembly, FORTRAN, LISP, COBOL, BASIC, MSBASIC, Pascal, Forth, C, C++, VB, VBScript, Java, JavaScript,LotusScript, C#,
Display or file format languages - HTML, HTML5, CSS, XML, JSON
Scripting in MS Windows and Unix.
Query languages - SQL, MSSQL, T-SQL,DMX, XQuery, SOQL,SOSL
Formula languages in Excel, Lotus, and obviously SF. 
Currently Apex, Visualforce, , and now learning lightning under SF>

So no matter which way you jump, there will always be learning.