However, there is nothing that says you must include your date of birth on a CV - so you don't need to include it if you don't want to. If you are worried about sounding too old then you should ensure that your CV makes you sound like someone who is energetic and vibrant, rather than old and frail. The actual wording of your CV is far more crucial than your date of birth. If you make sure your CV stands out from the crowd then your actual age really is irrelevant. Make sure you describe your time abroad positively so that an employer can see what benefits you have derived from the experience in terms of your personal development.
Many advertisements require the inclusion of salary history.
If you fail to include your salary history when it has been requested then you may well have your application turned down for failing to comply with the advertiser's request. So it is normally safer to include your salary history as long as the job is paying a similar salary to your existing job. In your case, however, it is more difficult for you to compare the salary you have in Belgium with what it might be in the UK or US, due to currency fluctuations, different tax regimes, differing costs of living, etc. I would be inclined to state that you don't feel that including your Belgium salary in the covering letter would be appropriate. My CV is 5 pages long.